For lots of gory details start here: http://www.webtrenches.com/post.cfm/adobe-coldfusion-9-hotfix-apsb12-06-causes-problems-with-large-forms.

Solution is to locate the neo-runtime.xml:

{ColdFusion-Home}/lib for Server installation

OR

{ColdFusion-Home}/WEB-INF/cfusion/lib for Multiserver or J2EE installation.

Find this line:
<var name=’postSizeLimit’><number>100.0</number></var>

Add or edit the line below after the one above, change 100 to what ever works for you.
<var name=’postParametersLimit’><number>100.0</number></var>