I wrote some code with the SDK and tried to test the SDK programming
example "Uploading a file to sp from a local folder".
When I try to upload a file to a sharepoint site (using the SDK
code), I receive following error:
"The security validation for this object is invalid". I checked
security settings and I am logged in a administrator, so this should
not be the problem. I also registered the FormDigest correctly,
because the problem only arises when I try to upload to sites
(e.g. "http://localhost/sites/uploadsite/shared documents/file.txt").
If I upload to a portal area
(e.g. "http://localhost/uploadarea/doclibrary/file.txt") is works
perfectly fine.

Did enybody experience the same problem? Would appreciate some help
here!