Users cannot create My Site; Access Denied

I discovered today that the limited number of users that are allowed to create personal sites cannot. They receive an 'Access Denied' error if they try. I am apparently the only one who can but I am a Farm Admin.

I have checked and re-checked the setup and cannot find anything wrong.  Self-Service Site Creation is turned on for the MySites web application and the User Profile Service application user permissions are configured using Active Directory security groups for the users in question.  The groups have Use Personal Features, Create Personal Site and Use Social Features enabled.

I have run the stsadm -o sync findolddatabases and the deletolddatabases commands on the Central Admin server under the Farm Admin account and run a full profile synchronization but the problem persists.

Thanks in advance for your help.