Overview:
A Validation Rule containing the field RecordType.Id is applied online, but not offline. The rule may fire when the offline device attempts to sync.
Root Cause:
The RecordType.Id field is a Salesforce metadata-only field and is not supported offline.
Solution:
The RecordType.Id field in the Validation Rule should be replaced with the RecordTypeId field on the object for which the Validation Rule is active.
Related Documentation:
CRM Help Documentation: Offline Validation Rules