Executing the next statement gives me SQL error -902 Internal error.

UPDATE MyTable
SET MemoField = :MemoField
WHERE (UniqueField = :Old$UniqueField) AND (MemoField = :Old$MemoField)

It seems this is caused because MemoField is a (text) blob field; updates to
other field types give no errors.

I like to use this statement to be sure MemoField is not changed by another
user.

Is the use of blob fields as parameter in the WHERE clause not supported by
Firebird 1.5 (WI-V1.5.0.4290), or is my construction wrong?

Thanks,
Robert
-.-