SPS2001: Getting an error when uploading the file, while upload eventually goes through.

Hello, fellow Experts!
Hopefully, you'll be able to help me.

I have recently copied our SharePoint Server 2001 to a new server (with plans to remove it from the first server, which will be then used in a cluster - but that's irrelevant).

Environment:
Windows 2004 + SP4 + MDAC2.8 SP8 + Update Rollup For SP4
SharePoint Portal Server 2001 + SP3
no other apps except for standard Win2k server package.

Getting an error when trying to upload a document or create a subfolder in Documents section - either through the web interface, or through the client.

When done through a web interface, after being asked to enter Profile information and such, I receive this error:

"An error occurred while processing your request. Please contact your system administrator for this server."

It does, however, let me upload the file... The file appears in the list of documents, and can be opened sucessfully, but none of the SharePoint-related actions or properties (such as Check-Out, Check-In, Delete, Rename) appear when I click on the Actions link. So basically, it sits there with me being able to do nothing with it.
If I browse to the folder where this file is, using SPS client & web folders, the file just doesn't appear there.

The same thing happens if I try to create a file using SPS client: it lets me create the file, but when I go to Properties-Security of that file, I get the standard 0x80040e21 OLE DB error. Moreover, the file just disappears from the folder list some 5 seconds later. I will be able, however, to see the file using the web portal interface, but once again, I can't do anything with it.

Thinking that this is the issue with the database, where the reference to a file is created, but not completely, i ran both ESEUTIL database check and ISINTEG -fix -test alltests. The ISINTEG returned several warnings and said it fixed them, about Folder not being consistent with Messaging Folder, in the same folders where I tried to upload files. But upon browsing to those folders, I am not able to do anything with the files.

I can, however, do normal sps operations (checkin-checkout-publish-whatever) with the files which were in the database prior to the move. I just can't add anything new.

I AM aware of the following Microsoft KBs, and, as I understand and tried their solutions, they are not related to my problem:

Unable to upload to Document Library folder, rather than it's Documents subfolder
Unable to upload ASP files
Unable to upload files with a long filename to a path with a lot of subfolders.

I am NOT the only person to have this problem, and I saw similar posts on usenet and google groups, dating back as long as 3 years ago, but not a single one of them had a reply with a solution - not that I could find:(

Reinstalling SPS anew is not an option, since there's so much information, files and documents imported in there already.

Thank you for your help.