I have a C# program that creates a .csv file and emails it.
Recently the client asked to have it run automatically, so I added to function to an .exe that is fired periodically by a custom Windows Service.
If I log in to the client's machine and click the .exe all goes well.
However, when the service fires the .exe, we get the following error:

Prowler Error- 03/28/19
at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
at System.IO.StreamWriter.CreateFile(String path, Boolean append, Boolean checkHost)
at System.IO.StreamWriter..ctor(String path, Boolean append, Encoding encoding, Int32 bufferSize, Boolean checkHost)
at System.IO.StreamWriter..ctor(String path)
at AnalysisClassess.AnalysisMethods.SendPickupData() in q:\ssprowlersource\AnalysisClasses\AnalysisMethods.cs:line 188
at AnalysisClassess.AnalysisMethods.ExecuteReview(DateTime lastreviewdatetime) in q:\ssprowlersource\AnalysisClasses\AnalysisMethods.cs:line 105
at ssprowler.ProwlerMethods.StartApp() in q:\ssprowlersource\ProwlerMethods.cs:line 56

It seems to indicate that there is some kind of privilege issue with the file creation.
Any ideas?