Comment 9 for bug 737615

@Thomas, In my case, in order to have the "Apply" button available again, I have to go to the "IPv4 Settings" tab and either enable DHCP OR (if i set it to manual) enter at least one VALID row (Address, Netmask, Gateway) in the "Addresses" table. Make sure there is at least one (usually one and only one) row of addresses and that all of them are valid. In my case, when this is ok, the Apply button is available again. Also, any other invalid value entered in any other field usually causes the Apply button to grey out and it becomes available again as soon as everything is valid.

Anyway, this still is a bug. because
1. saving a configuration with some invalid value is either allowed or not allowed. If it is not allowed, then it is absurd that you open a previously saved network and it is already invalid. If it is allowed, then you should be able to save it regardless of whether what you put is valid or not (and then you should get an error message when you try to connect to that network, or a warning when you save it).
2. If it is not allowing to save it because some value is invalid, it MUST tell you which one is wrong. It can't just refuse to save and not give you a clue. Not in the 21st century.