Worklist is being currently being processed by user XXXXX

Hi,

One of the user's ID is 12345 and when he logs on to UDM_SPECIALIST is gives the error "Worklist is being currenlty processed by user 12345" (his ID only). SAP gui was force quite and not other SAP sessions were open

If I double click the error it gives Message no. UDM_WORK_LIST033

Anybody has any idea what needs to be done and why user is getting such error?

Thanks