Unable to break role inheritance

A customer had a problem to break the inheritance from the parent web. The error message on the first page was "500 Internal server error" and when breaking the inheritance from Site Settings was:

“Cannot complete this action.
Please try again. at Microsoft.SharePoint.Library.SPRequestInternalClass.ResetSecurityScope(String bstrUrl, UInt32 dwObjectType, String bstrObjUrl, Guid guidDoc, Boolean bUnique, Boolean bCopyRoleAssignments, Guid& pguidScopeId, Int32& piError)
at Microsoft.SharePoint.Library.SPRequest.ResetSecurityScope(String bstrUrl, UInt32 dwObjectType, String bstrObjUrl, Guid guidDoc, Boolean bUnique, Boolean bCopyRoleAssignments, Guid& pguidScopeId, Int32& piError) “

Inspired by this solution I just broke the inheritance of the permission levels and inherited it again to fix the issue of not being able to break the role inheritance.

Fast recap:
Browse to http:////_layouts/role.asxp
Break the inheritance
Enable the inheritance again

// Henrik