Equation Engine error

I am receiving similar error with a SF Tuition Calc equation engine.  

Sql parm miscount in equation% eq% near line% 1% called% sql_variable% (14460,354)

screen shot of a portion of the eq eng.

The 2 sqls compare number of online classes vs overall classes to return a 'Y' if they equal when all classes are online classes.

Below is sql that looks for these counts.

This is the sql for number_of_classes:

SELECT COUNT(A.CLASS_NBR)

FROM PS_STDNT_ENRL A

WHERE A.EMPLID = :1

AND A.STRM = :2

AND A.INSTITUTION =

AND EXISTS(SELECT 'X'

FROM PS_CLASS_TBL B

WHERE A.INSTITUTION = B.INSTITUTION