Error: Illegal characters in path

[Shirin]

Hi,

I have a problem in CreateTxt.

strFileName = "500" + aHeader.Scheme_Code + aHeader.Sequence_No +
".pay";
streamWriter = File.CreateText(this.strPath + "\\" + strFileName);

It returns error 'Illegal characters in path'
and I found that it's only occurs in my PC. The problem dose not occur
in others PC. And when I got step in the debug mode, I've found that
the strFileName dose not with the file extension '.pay'. Please help.

Shirin