Problems InstallDir und SetOutPath $INSTDIR\test

Hallo again,

i have a strange problem i can not understand ...
In my script, there is an installer instruction:

  InstallDir "C:\Test\MyApp"

In an Installer Section i extract many files:

SetOutPath "$INSTDIR"

File /r "${ANY_DIR}\test\*.*"

I tested it many times and many times all was good. But suddenly the installer generates following error:
Error opening files for writing.

So i tested an other instdir --> all good --> and suddenly the same problem!
It's magic. I can not understand.

I work with Windows 7. Does Windows lock my C:\?

Thanks for helping