I was recently testing a scenario where the CRM 4.0 server was upgraded to CRM 2011 while the CRM Outlook clients were kept at CRM 4.0 for a period of time. I found through my testing that all CRM Outlook clients that had Outlook 2010 installed had their Offline, and Outlook filters grayed out after the server was upgraded; customers could experience this issue in both CRM on premise and online environments. I've included a screenshot below that shows the grayed out filters below: 

There are two workarounds if you find yourself in this scenario:

1. Upgrade your CRM Outlook client to 2011
   • While running CRM 4.0 Outlook clients against a recently upgraded CRM 2011 server is supported, we don't recommend this configuration as a long term solution.  A best practice is to upgrade to CRM Outlook 2011 clients as soon as possible.
2. Use the Options menu item
   • Even though the Offline filters and Outlook filters are grayed out in the drop-down menu, you can access these filters through the Options menu item (screenshots below).

- Jon