"Parsing form data failed" error occurs when logging in to a Web Client. After trying one or two more times, eventually log in succeeds. "Parsing form data failed" error when splitting a documents, or deleting a document's page via Web Client. This issue has been observed when using Internet Explorer 9 on Windows 7 (SP0 or SP1).
This issue can occur after you visit an NTLM authenticated shared folder. Microsoft Internet Explorer requires NTLM authentication for all visits after you visit one NTLM authenticated folder.
- To enable Kerberos Authentication set the EnableNegotiate Registry DWORD key in "HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings" to '0'.
- To disable Pre-Authentication in Internet Explorer create a DisableNTLMPreAuth DWORD (32 bit) key and set it to '1' in the same Registry location.
For further reference check the Microsoft Knowledge Base articles below:
You cannot post data to a non-NTLM-authenticated Web site
An unexpected 401.1 status is returned when using Pre-Authentication Headers with Internet Explorer and Internet Information Services
6.2 Service Pack 2