I know nothing about Informix, but "Value too large to fit in a SMALLINT" seems pretty clear to me.
A quick search with Google reveals the following page, that explains the max. values that you can store in a SMALLINT
http://publib.boulder.ibm.com/infocenter/idshelp/v10/index.jsp?topic=/com.ibm.ddi.doc/ddi159.htm
You need to change the datatype for the SMALLINT column to INTEGER, or store smaller number.