User unable to submit vaactaion in LOA page in SSHR

 Some users are getting the error below when attempting to enter vacation however i have not been able to track down why.  Any one experienced this error?  The formula is custom code but has worked for years and now users (not all) get the error.

The formula BG_ABSENCE_DURATION could not be executed because the context ASSIGNMENT_ID was not set. All the relevant context values must be set before a formula can be executed. Action: If this is custom code then please ensure that it sets all the appropriate context values. If this is not custom code then please contact your local support representative.