1. Line 70 of that file in the release-version of v1.5.4 says:
Code:
        set expiry = '" . zen_db_input($expiry) . "', value = '" . zen_db_input($val) . "'
2. You said this "huge session value" occurs when "trying to POST".
I'm assuming there's nothing significant about "what" you're trying to POST, and that it happens on "any page" instead of isolated to just a specific page, else you would have mentioned those details.
You also didn't mention PHP or MySQL versions.


I'm guessing that you've modified the cart in such a way that there's a ton of data being saved to $_SESSION variables, and if you wish to continue doing that (not recommended) then you may need to increase both your MySQL configuration for max bytes and your db table definition for the 'value' field ... and perhaps more things caused as side-effects.