(Finally I managed to open this forum on my PC - usually I open it on the iPhone and there I cannot open text file attachments.)
Hi, newbie or not, I still think there is some problem on your PC(s). I found this link:
SPIRIT ERROR C000035a - iPod touch, iPhone, and iPad forum - Multi-Touch Fans
You can also search Google for the error code (c0000035a) and the first hits are all Spirit-problems related. Most say that there are dll problems on the PC. If you have the same problem on several PC's maybe you configured them all the same way. Sorry, I cannot help more right now.
You might also want to try Spirit Fixer (I think it just renames the iTunes dll or something).