You are right Doroteja, "Fix the document" is not the best solution. I get used to press ctrl+z or Cancel as long as it is necessary to close the current segment with the corrupted tag, and open the previous one. It really helps.
Trados Fix Document command is good, but it can cause problems with document formating - i.e. spaces between lines, paragraphs, because some hard returns can lost if yu close segment in such way. In such cases I try to insert hard returns manually, or manually format cleaned file.
If you can not close sedment, it's possible to use ALT+F8 and select reset document from Macros.
I wish you success!