I installed the multi_variants addon for OpenERP v7 from launchpad: bazaar.launchpad.net/~anybox/openerp-product-variant/7.0/files
Once installed, a new checkbox appears in product forms, called "Is Multi Variants?" The problem is that this checkbox is disabled, I can no check it even in the edit mode of the form. How to enable this checkbox and start working with multi variant products? Thanks.
If I install next other branch:
~atin81/openerp-product-variant/openerp-product-variant
I can see now Templates and Variants menus in Warehouse > Products, but when I try to create a new template I receive next error:

The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request POST /web/dataset/call_kw.

Reason: Error reading from remote server