Saw this error pop up irregularly at a client’s site recently. It appeared as though something in Excel Calculation Services (ECS) was causing the Internet Explorer Request header to grow to a size that was larger than what the Web Front End server was prepared to handle.
I did not get an opportunity to investigate the root cause (deadlines were looming) but I believe the error was Kerberos-related (as it appeared after we enabled Kerberos) and that it had something to do with the 20-odd windows open to related ECS pages from the same site (perhaps the Kerberos ticket grew to a size that stopped it from working). The problem went away by using a new browser window, so the issue was session-based as well.
Finally it appeared to affect a specific account which was often used for testing, and as a result was a member of a lot of groups in AD.
After adjusting both of these registry values from 32767 to 65534 (FFFE) the problem went away.
The 2 registry keys to fix this issue are:
64 – 65534 (64kb) bytes
Sets an upper limit for each header. See MaxRequestBytes. This limit translates to approximately 32k characters for a URL.
256 – 16777216 (16MB) bytes
Determines the upper limit for the total size of the Request line and the headers.
Its default setting is 16KB. If this value is lower than MaxFieldLength, the MaxFieldLength value is adjusted.
There’;s a comprehensive post that exactly describes this issue and outlines the reasoning behind the changes – worth a read… http://blogs.technet.com/b/surama/archive/2009/04/06/kerberos-authentication-problem-with-active-directory.aspx
Have a great weekend!