Using File.IO.Move()

varA = "c:\\temp\\folder\\output\\file12345.dat"
varB = "c:\\temp\\folder\\error\\file12345.dat"
File.IO.Move(varA, varB);

When i try to use above code within an orchestration I get an error saying, 
Inner exception: Illegal characters in path.

It works if i hard code the location strings. Is there anything I am missing 
out on?

Thanks...rp