JESS: [EXTERNAL] Jess exception: ' ' is a list, not a string

I am receiving the error in the subject line when one of my rules is
firing. I can't seem to find any other forum posts about it, here is my
rule:

(defrule build-supply-depot
(minerals (value ?x&:(> ?x 100)))
=>
(try
(foreach ?u (?*bwapi* getMyUnits)
(if (= (?u getTypeID) ?*SCV_ID*) then
(bind ?p (call get-next-build-tile()))
(call ?*bwapi* drawCircle ?p.x ?p.y 100 111 FALSE FALSE)
(call ?*bwapi* build (?u getID) ?p.x ?p.y
(UnitType$UnitTypes.Terran_Supply_Depot ordinal))
(break)))
catch
(printout t (call ?ERROR toString) crlf)
)
)

and here is the exact error message:

        while executing (foreach ?u (call ?*bwapi* getMyUnits)
                                   (if (= (call ?u getTypeID) ?*SCV_ID*)
then
                                   (bind ?p (call get-next-build-tile ))
                                   (call ?*bwapi* drawCircle ?p.x ?p.y 100
111 FALSE FALSE)
                                   (call ?*bwapi* build (call ?u getID)
?p.x ?p.y (UnitType$UnitTypes.Terran_Supply_Depot ordinal))
                                   (break))).

  Message: '' is a list, not  a string.

But the error doesn't give me a line number.

Any help would be appreciated.
Thanks,
Hunter McMillen