Unfortunate, that's gonna make it difficult to narrow it down.
In such cases I utilize Microsoft Process Explorer for trying to reverse engineer what TBC is doing, which files are being accessed etc..
Now we have to see if there is anything out of the ordinary that makes TBC stumble
Is this a new computer, or the same where you say that previous versions did successfully import T-files?
(I always keep older TBC versions since there is pretty much always something wrong with a newer version - see post 4 here Trimble Business Center 2024 truncating feature codes | Trimble Business Center)
Can you send me the project file with which it fails.
When do you get the error message, immediately after dropping the T-file, or do you see some activity/progress bar before it returns the error?
What country settings are you using?
Any special characters in any of the files/folders? Including your C:\Users\ folder, TBC is writing things to the AppData folder. There had been issues with Scandinavian characters before and since your data is located in Sweden that could be a possibility.
Where is your project saved? - folder name
Where is a new project created before you save it someplace else? - the project management folder

What coordinate system settings do you use?
In "C:\ProgramData\Trimble\GeoData", do you see a subfolder "G"? It should not be there, that was an error with some older installations. The cleanup utility should have taken care of it as well.
Any out of the ordinary files or folder names directly on your C-Drive? There had been an issue for example with exports for machine control when a mouse software had created a file "program." in "C:\".