I have a number of files in a folder, and I need to get the last modified date. So I used
FDate = IO.File.GetLastWriteTime(FName)
It works fine
From File.GetLastWriteTime Method:
If the file described in the path parameter does not exist, this method returns 12:00 midnight, January 1, 1601 A.D. (C.E.) Coordinated Universal Time (UTC), adjusted to local time.
The file you are querying is probably missing.