Find absolute path on file opend by another software

Hello
In first time, i apologized if my english is not good.

I build a software which needs to found the absolute path of a file opened by another software (regardless which software is). I found the "OpenFileFinder.dll" which can found them.

But, unfortunately, some time, the dll don't find the file and if i restart the scan do by the dll, he found the file.

Is anyone knows this dll to tell me if this instability is due to windows (i use win xp for the moment but the code change for can be used on vista, 7 and 8) or is due to the dll. And if you know an alternative to restart 2-3 times for finaly found the file, i read all your solution (except scan of all hard-drive because i need to find it in few second, regardless how many drive exist)

i work on VS c# 2008 in framwork 3.5

thanks

Nicolas