Update, case, and -407

The following (skeleton) works fine when using AQT (win/xp, ODBC),
but throws a -407 when issued from green screen SPUFI.  The DB is 8.1.5
on z/OS.

update tableFoo
set colFoo =
case
    when otherFoo = 'A' then 'B'
    when otherFoo = 'C' then 'D'
end

Any notion why?  Couldn't find an APAR or any explanation on
the DB2 site.

thx