The processing of Group Policy failed

I keep getting error like the following in the event logs of my clients and GP is not being processed. Why? The Error: Windows cannot access the file gpt.ini for GPO cn={6AC1786C-016F-11D2-945F-00C04fB984F9},cn=policies,cn=system,DC=cpandl,DC=com. The file must be present at the location <\\cpandl.com\sysvol\company.NET\Policies\{6AC1786C-016F-11D2-945F-00C04fB984F9}\gpt.ini>. (Access is denied. ). Group Policy processing aborted.

There are several reasons that I've seen that cause this error. In cases where computer policy processing is failing with this error but user policy processing is occurring just fine, it could be a network stack timing issue. In that case, check out http://support.microsoft.com/default.aspx?scid=kb;en-us;840669

In cases where its just failing outright for all policy there are at least two other possible reasons for this. The first is that one or more SYSVOL replicas on your DCs are not replicating correctly and the gpt.ini file is actually missing from a given DC that the client is hitting. In this case, Windows is not smart enough to failover to another DFS replica (SYSVOL is just a system-maintained DFS replica) and GP processing will simply fail. In that case, the quickest solution is to copy the contents of the failing GPO from a known-good copy of it on another DC. The last reason I've seen for this failing is when you've implemented a restrictive security policy on the client that is processing GPO. For example, if you implement one of the "High Security" templates from the Server 2003 security guide, which may require, for example, SMB signing of all network traffic between server and client. In that case, if the server does not support that requirement, basic file communications between the client processing GP and server will fail. Usually the solution there is to apply a less restrictive security template to the client processing GP (or to the DC serving up GP if the change was made on the DC side)