UDFs disappeared

Dear All

I am facing a problem in one of our client. If any UDF is updated by user1, user2 got the message 'Database structure has been modified.....'. When User 2, select 'YES' or 'NO', then all the UDFs in marketing documents or User tables, disappeared.

However, if we access User Defined Fields window, UDFs are appearing there. But not showing in any marketing document.

Kindly help to resolve this.

Regards

Nabeel