>>>I know this will sound obvious but did you try making a second copy of the report form into a different directory and then opening that one? Then try to change to attributes of the copy? What you describe happened once to me and this copy move helped. Can you delete the current file?
>>>
>>>Alan
>>
>>Great advice!!!!!!!! Yes, I copied this file to another directory and opened it without problems. How didn't I think about it by myself? :)
>
>Again, can you create a text file in the directory?

Yes. We just found a problem and fixed it. The server machine had to be re-booted (it probably crushed and hold this file somehow). After we re-boot the server machine, I can open the file without problems. But this one really costs me some bitter minutes...

Thanks everyone for the help. Next time we'll start from re-booting :)