Many problems with Pay Per View

on WP 3.4.1 i have a lot of problem with Pay Per View.

i've tried to make transations with the sandbox but i get always the same error:

10002 – Security error – Security header is not valid

I've read a read a thread on this site, but the proposed solutions don't work for me (and i've controlled paypal datas many times).

Another problem is that the pay per view dialog doesn't appear in new posts and posts remains entirely visibles. The plugin is configured to make premium all posts, and it doesn't work anyway, if I insert manually the dialog in the content of the posts.