Why I am getting a fllename or volume or label syntax error incorrect on reading file via continuous service installed in IIS 7.5?

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C#2.0

C#

ASP.NET

IIS7.5

Why I am getting a fllename or volume or label syntax error incorrect on reading file via continuous service installed in IIS 7.5?
I am running a windows service installed in server. I am fetching files from a folder and reading and moving the file from source folder to destination folder. But sometimes I am getting "Filename or volume or label Syntax Incorrect Error".There are other service also running at times. In local while running no such error seen.
My code is as follows:

strmDirectPIF = new StreamReader(DirectPIFToBeDonePath);

                    while ((PIFRecord = strmDirectPIF.ReadLine()) != null)
                    {
                        words = PIFRecord.Split(',');
                        if (words[0] == "EDR")
                        {
Read the file content
}
   strmDirectPIF.Close();
                                                        MoveFile(DirectPIFToBeDonePath,DirectPIFDonePath);