If you upgrade to Microsoft Dynamics CRM 2013 and you find that one of the Command Bar buttons don’t work, reset the ribbon for the entity.

1. Create a solution that just includes the entity with the button that isn’t working correctly and export from CRM.
2. Extract the customization zip file.
3. Open the customization.xml file in the editor of your choice.
4. Search for RibbonDiff.
5. Replace the entire <RibbonDiff> section with the following:

<RibbonDiffXml>
 <CustomActions />
 <Templates>
 <RibbonTemplates Id="Mscrm.Templates"></RibbonTemplates>
 </Templates>
 <CommandDefinitions />
 <RuleDefinitions>
 <TabDisplayRules />
 <DisplayRules />
 <EnableRules />
 </RuleDefinitions>
 <LocLabels />
 </RibbonDiffXml>

Save and zip up the solution, then import and publish in CRM.

Credit to the Power Objects blog for a variation of this tip for CRM 2011.