Thanks for the idea, but having rewritten the statements into portions, the error vanishes (being replaced by DATETIME problems, but that's another story!), so looks like DBD:ODBC has some significant issues.

BTW: I'd tried the ? placeholders, but SQL server simply doesn't do them! Or perhaps the SQL interpreter in DBD:ODBC doesn't understand them....

adding finish() between each call has helped too, so thanks guyus for your suggestions (helpful or otherwise ;)