If you look in the installation directory, there's a mantisdebug.log file which is the primary log for the system.
I would suggest moving this file to another location and then attempting to upload a document.
The file should then contain information related to that action.
I would also ask that you submit this to the hotline. It is definitely something that development should look into.
When uploading a file i get this error- "upload fail- read error" I do not see anywhere where I can read a message about the error though, so if there is some where that describes the issue that Core has with the file, where would that be?
Why would it fail to upload in the first place?
Thanks in advance.