issues updating and downloading apps. error 3150

Over the past couple of weeks I have been having trouble both updating and dowloading new apps on my iPhone 4 and in iTunes. Some work perfectly fine but others just won't download, the size of the app does not matter.

On my iPhone it often comes up saying "unable to download application" when i press update or install and I get the option of "retry" or "done". Retry just leads to the same outcome and clicking done leaves the app greyed out with a loading bar at the bottom. If I click the app again the same thing happens. Deleting it and re-installing doesn't help either. Restarting the phone occasionally allows one to download but the next will have the same problem. this has happened both on my home wifi, on 3G and on uni wifi. I have now managed to download all the ones that were having a problem but would still appreciate some insight into it in case it happens again.

Now though, iTunes refuses to download many app updates, saying "network connection could not be established" and giving "stopped (err = -3150)" this happens for about half of the app updates. I have a good internet connection that doesnt randomly drop out so I don't know what is causing this either. I haven't changed any router settings and it always worked before.

It seems rather coincidental that it started happening roughly when the problems dowloading on my phone appeared.

I am using both the latest version of iOS and iTunes.

If anyone could help I would appreciate it!

Ruaraidh