Problem getting USPS Shipping to work properly.

So my site is fully setup/configured, and everything works fine with UPS, but when I try to use USPS, in conjunction WITH UPS or INSTEAD OF, it won't go to the next step (Shipping Method Select) when you click "Continue" at Checkout, and I get this error after clicking "Continue" when trying to do a test checkout.

PHP Notice: Error: Unknown column 'unit' in 'where clause'<br />Error No: 1054<br />SELECT DISTINCT weight_class_id FROM weight_class WHERE unit = 'lb' in /home3/johncpit/public_html/johnpittman/opencartnew/system/database/mysql.php on line 49

Any idea what this is telling me or how I resolve it? As far as I can tell, I have the USPS info entered/configured properly.

HELP!

I'm sorry that I can't help - but I am having the exact same issue. Have you figured out a solution?