Why do my friends act like this?

My friends have recently started to seclude me from certain things. Things such as not inviting me to their party on skype, or not inviting me over to a LAN party (like a video game party) When I confront them about having a separate skype party thing they deny it. The same thing for the LAN party, they deny it even though I knew they were having one. I still want to be good friends with them but this is really putting a wedge between us. ANY advice is appreciated.