How do I fix my Commerce Feeds import process post updating my modules and core?
I have the same problem. I think that is because I am using a old version Drupal Commerce and it is incompatible the newer version of Feeds module that i am using.

but I manage to get it work by paste in this function: 

function commerce_product_validate_sku($sku) {
  // Do not allow commas in a SKU.
  if (strpos($sku, ',')) {
    return FALSE;
  }

  return TRUE;
}


into the file "commerce_prouduct.module" located in:

{mydrupal-installation}\profiles\commerce_kickstart\modules\commerce\modules\product


I found that function in:

http://drupalcontrib.org/api/drupal/contributions!commerce!modules!product!commerce_product.module/7

Hope that help! 

Apollo Tang