[Zope] storing blob data in SQLServer using ZSQL

Hi, How can I save blob data in SQLServer using ZSQLs? I'm using mxODBC. I have a ZSQL that looks something like this:

update table_name set blob_data = <dtml-sqlvar "i_blob_data" type="nb"> where conditions.... But I get the following error when I run the above ZSQL:

ProgrammingError: ('07002', 0, '[Microsoft][ODBC SQL Server Driver]COUNT field incorrect or syntax error', 6108)

Any comments will be much appreciated. thanks, Satchit