Validation Message States Value was Either too large or too small for an int32 in ASP.net 2.0 Webform

Good Afternoon,
I've "inherited" a web application written in ASP.net 2.0 VB 2005.  A textbox, named txtQuantity, has a required value validator and a regular expression validator on it, with a maxlength of 14.  The class library defines txtQuantity as Long and the destination SQL Server 2005 database field is of type varchar (20). 
When I test the form on the production server (GoDaddy), I receive the message Value was either too large or too small for an int32.  However, this validation text is nowhere to be seen in the .aspx or codebehind pages.  I note that the original developer added assembly references for Free Textbox and Anthem.  So, I'm thinking this might be a Javascript validation?
Has anyone received this message in a ASP.net 2.0 web form?  Can it be triggered through javascript validation?  If so, how is this remedied?  Through the assembly or thro ...