MSA - creating/changing activity for bp error : enter a valid value for bp

Hello experts,

while using msa with activites, on one client for one bp

I cannot create/change an activity: error:

insert a valid value for bp

This happens only for one bp on this client,

on other clients this bp works fine.

When I look in old activites for this bp, there in activity -> detail

the field bp (hyper link) is not filled.

I think there is a problem with the incorrect bp, but in which tables

can search for this ?

Best regards

Gerd