problem TC with internet under EL capitan

Since i installed El Capitan I have the following problem:

I have an Time Capsule which I use (exclusively) as an External hard disk, to save space on my Macbook Pro. The internet I use through the home network (which is different than the TC);

If I plug in the TC now I can't use the internet. If I remove the TC I can go back on the internet (sometimes I need to reset the Wifi connection).

This is rather annoying. I don't know what the solution could be....