I believe this is a variant of issue #547 -- i.e., I suspect the cause is the same.

I could not get sclang to work well in XP unless it was built with no compiler optimizations (meaning, impaired performance in the language). I believe we'll need an expert Windows developer to fix it properly. Unfortunately, we don't have an expert Windows developer in our community. Well, Victor Bombi has done some work but mainly scsynth and supernova.

That means for now, XP is unfortunately not supported.

OK, thanks for your reply !

This issue does not occur anymore on a SC3.7alpha build Win32. built in MinGW64 gcc 4.8 QT4.8.4. The probably related TempoClock issue #547 is gone too.

good news ! can't wait for the final build

Well, mine is a private build. No signs yet as to whether the maintainers of the official build are going to update their toolchain soon - they might have a policy only to use official MinGW and QT releases, or they might simply have no time. My build uses MinGW and QT from "mingwbuilds", which on a slightly smaller scale seems to relate to MinGW a bit like Ubuntu relates to Debian - use their stuff but race ahead ;).
I'm happy to provide you or anybody else interested with the binaries and/or the build environment I used. I am very interested in feedback on it's merits and especially shortcomings, as I expect to use SC on Windows XP in Indonesia a lot next year.

I don't remember if this was just Windows XP related or a general Windows problem. The problem does not occur master/Qt5/Win 8.1 any more. Generally speaking I think Win XP support can be dropped for 3.7.

I agree -- close all XP-only issues. If Microsoft doesn't support it anymore, then we don't have to.

Closed because Windows XP support is dropped