iis 7 permissions error

[m.dangelo]

I just bought "Unlimited Sitemap Generator" but I can not run it on IIS7 on which it is properly installed the php interpreter.
Always gives me this error:
"An error occured
These files Error writing to:
C: \siti_interni\navis.it \generator
Please correct file permissions and resume sitemap creation. ".
all write permissions seem ok. Can you help me?

[XML-Sitemaps Support]

Hello,

replied to your email.