Systems gets held while using Skype

I encountered error with the Skype and the 2011 Multipoint server. When I have set up the Skype, and use this programs I notice that I freeze every now and then. Also when I use the Excel, had a same situation. Is the Skype has a connection with this error like freezing the program. Is there anyone has same problem with Skype and how could I resolve it? However, when I am not using Skype the computer works normally but when I am going to use the Skype same error I experience. Please help and thank you.
