Thanks for your help.
First error was on Win XP, next day it appeared on a Win 2008 R2 server.
I already re-generated the MSI files and deployment tasks - does not change anything
Maybe manual MSI package helps, I will give you feedback on that one later.
//edit 1:
I just remote installed another Win XP client without any problems - package seems to be okay.
//edit 2:
Manual MSI install worked fine on the Win 2008 R2 server.
Problem is not solved but now I have some kind of workaround - thanks again.