Can't upload attachments anymore
 

I just install and ran vbseo sitemap generator. Then i found my forum no longer can upload attachments. The "Manage Attachment" window will appear just fine. It is only after a file is selected, click on "upload", an error message appears.

Error message: ["vBulletin Message: Invalid Post specified. If you followed a valid link, please notify the administrator"]

I have no clue what when wrong. Anyone have the slightest idea? thank you in advance