A few days ago a client had the upgrade scheduled from CRM 2013 to CRM 2015 online, and when they wanted to create an opportunity product (not with the standard relation but with a new relation that we created so it only appear the existing product selected), it wasn’t possible because the new permissions weren’t configured.
We had to go to the profile role of the users that couldn’t access and then add the read permissions to the profile:
It was also necessary to add the permission to be calculated by the system, because this was not configured for.
Going to Settings -> Administration -> System Settings in the Sales tab has the following option that should be Yes.
This might help someone later!