Re: SQL problems SQLSTATE 42601 - 104 on Execute Immediate

I was testing an sql Execute Immediate that has been in Production
for a while now, and found that it was failing with SQLSTATE= 42601
and SQLCODE = -104. Seems like there's a syntax error, but when I
copy the statement from the host variable, and paste it into
interactive sql (strsql), it updates the record just fine.

The statement is:
EXEC SQL
EXECUTE IMMEDIATE :UpdateSQL;

The value of UpdateSQL (as copied directly from the variable value
in debug) is:
UPDATE PLTLCD
SET LCDSCM = 'ADSL Dynamic 0004780533 '
WHERE substr(LCDSCM, 6, 23) ='Dynamic 0004780533 '
AND LCDSTY = 'ADSL '
AND LCDSTS<> 'D'
WITH NC

Is there anything about that statement that would behave differently
in the Execute Immediate environment?

This is failing on v7.1 -- I believe we're up-to-date on PTFs.
It's probably me -- can someone enlighten me?