Object reference not set to an in stance of an object

I ran into strange trouble trying to translate a file in a project package: I received the error message above when I tried to edit a segment normally and suddenly the program does not let me edit any of the file. I also got more error messages referring to corrupt memory, but I could not repeat them after I closed the program and tried again.The problem is related to one single segment. When I reopen the file I am able to edit other segments, but touching the segment in question repeats the problem, and I cannot edit anything after that.

I would appreciate any suggestions or ways to get round the problem.

Regards,

Suvi