For starters move the .tbb file fr om the inbox. Don't delete it, but store it at another location.

TB shouldn't have any problems anymore with over 2GB in a single folder, but 4 GB is rather large. When was the last time you compressed it?

What OS and virsus scanner are you using and what file system on your hard disk?

The warning about the .tmp that couldn't be stored can point to two things, hard disk full or infected by a virus and blocked by your virus scanner.
What's the amount of free space on disk?

Presuming you've got plenty of free space, I'd suggest that you pick fr om the menu:
Tools -> Import messages -> From TB message base v2 (.tbb) and point it to the location of your move ibox .tbb.
Note that the messages are imported into the folder that's sel ected during the import command. So I'd suggest that you don't import them into your inbox or any already existing folder, but that you cre ate a new folder and do your importing there.
Note also that the problem might be virus related, so it might be prudent to disable your virus scanner during this procedure and after you've imported them you check the folder you've restored them to to see whether there are messages with suspect, odd or unanounced attachments and delete those messages and compress the folder afterwards.

As you're talking about a message base of 4 GB, I'd suggest that you take care of a free space amount of at least 8 GB both at the drive wh ere your message base is located and on the drive wh ere you store your temp files.

I don't know when was the last time you cre ated a backup, but if everything else fails, the messages that were included in your backup should be restorable.
So if you didn't disable TB's default daily backup your bacon should be saved as you keep new messages stored on the server too. (That's what you meant with your trash story, didn't you?)

However that messages deleted from trash won't be deleted from the server might mean that the link  between the account on disk and the account on server might be broken. For me that points to disk problems, but it could also mean that that was because of the break via the task manager.
Story about the daily backup goes here too.

I've asked it before, but when was the last time you compressed your message base. That's important especially in order to prevent your message base fr om getting overly large because.

What's the normal amount of messages in your inbox?
Can you access your account on server via webmail or such? In that case are there any messages with bizarre attachment sizes? (I'm thinking of over 100 MB)

> Thank you for the reply. What I did is this: rename the .tbb file
> to messages_old.tbb, and tried to import it into a new folder.
> However, the import operation has been running for over 4 hours now
> and it didn't even cre ate the messages.tbb file in the new folder.

Try it again, maybe overhight.
What  you  could  do  is  cre ate a new Windows account, setup a new TB
config  with  its  own message base, and let that instance of TB to to
import.  After  a  night or even a weekend you can see what's salvaged
and cut that into manageable portions to import in your main config.

> And to answer your questions: disk space is plenty available.

That's good.

> The folder was last compressed probably 1 month ago, and I believe
> its size is normal.

About compressing:
Mail  client (and databases) don't delete a message (or a record) when
you  tell  them  to.  They  merely mark it as read. Really deleting it
would mean they would need to rewrite the base file. (would take a lot
of time with your 4 GB file)
Moving  a  message  merely means that the message is copied to another
folder and that the original is marked as deleted.
Compressing  means that the message base is written again, without the
deleted files.

About the Inbox.
TB  receives  every  message  in  the  inbox. It can can be moved by a
filter  or  by  you,  but  it  arrives at the inbox. It can be deleted
automatically,  but  first  it arrives at the inbox. So the inbox gets
bigger and bigger (until you compress it)
Large files are more susceptible to corruption than small files
Files with a lot of writes to it are prone to corruption
That's two reasons to compress daily and not to use the inbox for long
time storage.
TB  has  this  great  filtering  system. Use it. That's the reason I'm
using TB anyway

You think 4 GB is normal?
My  main  account contains 114000 messages in over 100 folders, but it
uses  less  than 3 GB of disk space. Believe me that 4 GB for a single
inbox is excessive.

> Messages are indeed kept on the server for a period of time,

That's good, that means that you can download them again.

> but the biggest issue here is the message history in the folder on disk.

I'm  not  sure  what  you mean with that. I surely hope that you don't
mean that you move your outgoing messages into your inbox...


> I don't have the daily backups (for some reason I never saw it
> doing them),

That's a pity

> but I have regular disk backups.

That's good

> Unfortunately, the latest is two weeks old,

That's not so good

> and I would prefer to recover as much as possible fr om the emails.

You could download the latest batch again

> If it comes to that, can I just get the old .tbb and .tbn files
> from a backup and copy them into the folder?

Yep,  that  works  as  a charm. I'd do that with TB shut down. And you
might  want  to  restore the account.m_d and account.m_r files too (in
the  account  directory) That's wh ere TB keeps count of which messages
have been downloaded.
You  might want to store the files into a different folder and not the
inbox, just to prevent that the folder size is causing the problems.

> As for the cause of the crash, I don't have any disk errors.

In  that case, it might be the folder size, interaction with the virus
scanner,  interaction  with the firewall, problem with the mail server
due  to  the  long  period  of  the transaction, and simply killing TB
doesn't help the condition of its files.

Created  in  TB's  editor, as the forum keeps logging me off, before I
can type a real message.

In case yor computer is running for days you can cre ate an event in TB's scheduler that compresses everything at night.
Set the time at whatever you fancy
Set the recurrence to every 1 day(s)
St the action to 'folder maintenance' and you'll get a window where you can pick the folders and the types of maintenance you want to be performed.

At night the maintenance won't bother you.

The autobackup can be configured at:
Options -> Preferences -> System -> Auto backup
The time can be set at any given moment, so a time at night after the daily maintenance sounds as a good idea. (Though the same might be said about a time before your daily maintenance.)
A backup of 17.5 GB will take some time and TB freezes during the backup, so a moment at night is the smart thing to do.

Ok, I left it to run for several hours, and I got an 'out of memory' error.

Are there any other options at this point, or I should just overwrite the files with the latest backup?