(SQR 4407) Referenced variables not defined

Hi there,

Wondering if someone can explain what I'm doing wrong with this SQR. I think the problem is that each employee pulled on the initial select will have either &.A.Last_HIRE_DT or &A.LST_ASGN_START_DT depending on if the job is primary or secondary. I'm trying to pull whichever date is populated and assign it to the $lastHireDate variable but running into the 4407 error. Is the solution to determine if the job selected is primary/secondary then jump to a second procedure which only pulls the correct column variable? Any help would be much appreciated.