Try to Increase the value for the directive LimitRequestFieldSize in the httpd.conf:
Reason: This is normally caused by having a very large Cookie, so a request header field exceeded the limit set for Web Server.
For IBM® HTTP Server, this limit is set by LimitRequestFieldSize directive (default 8K). The LimitRequestFieldSize directive allows the Web server administrator to reduce or increase the limit on the allowed size of an HTTP request header field.
SPNEGO authentication headers can be up to 12392 bytes. This directive gives the server administrator greater control over abnormal client request behavior, which may be useful for avoiding some forms of denial-of-service attacks.