Sorry just missed the first line that u r using MySQL database.
for my sql convert functions parameters are
convert(expression,datatype)
or cast can be used as
cast(expression AS datatype)

datatypes
SIGNED {INTEGER}
UNSIGNED {INTEGER}

sqlcodmod="select convert(codmodulo,UNSIGNED) from modasg where cod='"&request("cod")&"'" 
   set rscodmod=conn.execute(sqlcodmod)