Was the product created programmatically or via import script?

If the configurable product doesn't have a value specified for the options_cointainer attribute, the effect will be similar to the one described by you.

You can solve the problem by saving the configurable product from Admin Panel, selecting a value for the the "Display Product Options in" of the "Design" tab of the product details.

Otherwise the following will do that programmatically:

 Mage::getModel('catalog/product')->load()->setOptionsContainer('container1')->save(); 

or

 Mage::getModel('catalog/product')->load()->setOptionsContainer('container2')->save(); 

Regards, Alessandro

Was the product created programmatically or via import script?

If the configurable product doesn't have a value specified for the options_cointainer attribute, the effect will be similar to the one described by you.

You can solve the problem by saving the configurable product from Admin Panel, selecting a value for the the "Display Product Options in" of the "Design" tab of the product details.

Otherwise the following will do that programmatically:

 Mage::getModel('catalog/product')->load()->setOptionsContainer('container1')->save(); 

or

 Mage::getModel('catalog/product')->load()->setOptionsContainer('container2')->save(); 

Regards