Our SharePoint 2010 Enterprise environment was recently upgraded to SP1 and the June 2011 CU. Came in this morning to a error form an Infopath form. After checking it out, I got the same error myself when switching views on a browser form:
“The security Validation for this page is invalid. Click back in your Web Browser, refresh the page and try your operation again.”
Ran the error through el Goog and ran across this TechNet post pointing the finger at a new OnLoad event in the June CU. The August 2011 CU supposedly fixes (removes) it. But we’re not there yet, so here’s another way to bypass the problem:
In the 14 hive, under template/layouts, find the formserver.aspx file.
Backup the file and then edit it with any text tool, say, notepad.
Under the <body> tag, add the blue line of code.
<body runat=”server” id=”PageBody”>
<SharePoint:FormDigest runat=”server” />
Save it and give the form another go, you should be good as new.