You cannnot express an UNC path like you did; and you have to escape backslashes (or put an @ to declare the string). The correct path is:
fileInDir = Directory.GetFilles(@"\\PARISA-PC\C$\OMEGA\KAJ", "*.Bmp", SearchOption.TopDirectoryOnly);
Or, without @:
fileInDir = Directory.GetFilles("\\\\PARISA-PC\\C$\\OMEGA\\KAJ", "*.Bmp", SearchOption.TopDirectoryOnly);