GPIO buttons problems

Hi, I’ ve build my Volumio Internet Radio and i’ m trying to include push buttons control.
About Volume up and down, no problems but…previous/next radio station (from the List “My Web Radio”) don’ t work.
I’ m using GPIO pins 2,3 for the Volume control and 4,5 for previous/next, connected to ground as shown in some guides I’ ve found.
When I push the previous station button, I read an error message on the UI; if I push the next station button sometimes nothing happens end sometimes I have to push “Play” again on the UI.
Do you have some suggestions about?
Thank you!