Error removing & reinstalling application?

I several weeks struggling with the problem one of my applications. When I try to repair (Repair) during this process it pops up a window: “the folder path ‘Documents and Settings’ contains an invalid caracters”. Before I decided to write this post I browsed the internet for this problem and have not found anything specific except MicrosoftFixit program, which did not help me. I made a disk defrag PerfectDisc and scan disk MHDD program. The environment variables are correct. I sense that this is caused by damage to the registry but I do not know how to check it out. I did restore the Registry First Aid but it did not help. I ran out of ideas and ask for a hint.