There are over 50,000 lines of code in fs2_open...if we knew exactly where the error was and what it said based on 'it doesn't work', chances are, the bug would've been fixed already.
Once the error message appears, you should be able to just open Notepad, then click "Edit->Paste". You don't have to copy the text; FS2 does it for you.
If that doesn't work, take a screenshot when the error is on the screen (Press printscreen...it will automatically copy it to the clipboard). Then open a program that can save to .jpg (Like
IrfanView), paste the screenshot into the program. Then save it as a JPG and upload it somewhere.
If even that doesn't work, copy it down somewhere. Most error messages have a message at the top, telling what the problem is. Then below that, they have a whole bunch of letters and numbers and crap that doesn't really give any info. Copy down the stuff that's in english and post it here.
If you aren't willing to spend 30 minutes to load whatever is causing the error so you can give us a decent description of the problem, don't expect it to get fixed.