Diagnosis
In the field selection for WBS elements, you specified that theinvestment program, approval year and position ID fields are allhidden. As a result, it is not possible to make any entries for thesefields here, which also means you cannot make assignments to investmentprogram positions from here.

System Response
The system does not let you assign the WBS element to an investmentprogram position from here.

Procedure
Assign the WBS element from the program position itself, or change thesettings in the field selection of the WBS element.