Ess - Mss Leave Request

Hi,

When applies for leave thru ESS portal and the request does go to MSS and

When Manager from MSS is trying to approve leave, he gets a message "collision with other time entry".

After thorough inspection, we don't see any leave applied on the respective date and manager is able to approve the leave but the message "collision still appears"

Why?

Pls advise

De-