Ok, thanks guys. Your various messages made me go back and look really hard at what I was doing before parsing the file, and I found that indeed, when started as a service, the path to the file-to-parse was incorrect.

Basically, when starting as a service, the startup directory is not the same as when starting in a console. My program "knows that", and does a chdir() in that case. But I ended up pre-pending the current directory path twice to my filename, and trying to parse "C:/XYZC:/XYZ/filename.ini" when running as a service.

Entirely my fault, but your comments were very useful in helping convince me that I was not the victim of some obscure Perl/XML-Parser/WinXP scheme.

Many thanks.