Here are where the MMS settings are located and what they do.
With regard to the Access point in use information. Go to your service provider's website and search for multimedia message centre settings and see if they are the same as what you have in the phone, in the Access point in use setting as stated below. Also check that the Multimedia Retrieval option is not set to Off.
Multimedia message settings:
Menu > Messaging and Options > Settings > Multimedia message.
Select from the following:
Access point in use — Select the default access point to connect to the multimedia message centre. You may not be able to change the default access point if it is preset in your device by your service provider.
Multimedia retrieval —
Select how you want to receive messages, if available.
Always automatic to receive multimedia messages always automatically,
Auto in home netw. to receive notification of a new multimedia message that you can retrieve from the message centre (for example, when you are travelling abroad and are outside your home network),
Manual to retrieve multimedia messages from the message centre manually.
Off to prevent receipt of any multimedia messages. Automatic retrieval may not be supported in all regions.
Allow anonymous msgs. — Receive messages from unknown senders.
Receive adverts — Receive messages defined as advertisements.
Receive reports — Request for delivery and read reports of sent messages (network service). Receiving a delivery report of a multimedia message that has been sent to an e-mail address may not be possible.
Deny report sending — Select Yes to not send delivery reports from your device for received multimedia
Message validity — Select how long the messaging centre tries to send the message (network service). If the recipient of a message cannot be reached within the validity period, the message is removed from the multimedia messaging centre.
Maximum time is the maximum amount of time allowed by the network.
If you can access the internet OK on your phone and YouTube is the only app that you are having problems with try the following and see if it resolves the YouTube problem
Go to Home > Apps > Settings, swipe to Device tap Apps swipe screen until Downloaded appears at top of screen, scroll down to find YouTube (if YouTube is not in Downloaded list, swipe to All and then scroll down to find YouTube)
Tap to enter YouTube, tap on Clear Cache option and follow the prompts. Once completed, return to the Home screen then try the YouTube app and see if works now.
If it still doesn't work, go back to the YouTube app as before but this time select Clear Data and follow the prompts. Once completed, return to the Home screen then try the YouTube app and see if works now.
Be aware that if you choose this option (Clear data), all your personalized settings for the YouTube app only will be reset to their default values. You may have to change the YouTube app settings to how you had it before.
Hopefully either one of the two above methods will resolve it for you.