Netware OES ,secure iPrint printer agents, Windows XP SP2, iPrint client

We had an iPrint server working successfully until today. Everytime a
user tried to authenticate this message would pop up in the Apache2
error log -

no acceptable variant: SYS:/Apache2/error/HTTP_UNAUTHORIZED.html.var

and the user would get an 401 unauthorized message from the iPrint client.

I could not see any obvious activity for the would be binds on the
target LDAP server specified in the ipp.conf file. I thought maybe one of my collegues had changed the ACL's
(longshot!)..nope. In fact there had been no changes to the server.

So I restarted Apache2 with AP2WEBRS.

Still no joy same error.

I checked the server health , memory etc, and all was fine.

So finally I restarted the print server and magically all started
working normally again.

Has anyone out there seen this error before? Its very disruptive to
service having to restart the server to get things working again.