Program error: ASSIGN with length 0 in program "SAPLLSO_RHVS""

Dear experts,

everyday when I check ST22 i find several times the same issue:

ASSIGN with lenght 0 in program "SAPLLSO_RHVS"

The user causes this error is always a participant of a course at the moment of accesing course in portal. Unfortunately I have no way to reproduce this case.

Do you have any idea about what could be the problem?

I would appreciate any suggestion.

Thanks in advance for your help,

Maria Jose Guart