Page Load Creating "Bad" values

I have an application which on the first page the user designates which reports they want via a long list of check boxes. On the next page (this is where Iââ?¬â?¢m having the problem) on the form load the application takes the various values of the check boxes that were selected, which are database IDs, and places their IDs into a comma delaminated list (i.e. 51,52,53) as a string.  This value is then placed into a Hidden Field so that it can be used by the application latter.  However when I post to a new page, while the system can find the Hidden Field, the result is always a null set.  I tried converting the hidden filed into a text box (thinking I was just getting the coding wrong for hidden fields) but the result is the same.  I ...