Having problems connecting with Skype?
The issue is most likely related to the recognition
of touch tones (DTMF – Dual Tone Multi Frequency).

This is a known issue by Skype – see Skype's forum thread

What should I do?
1. Keep trying to enter tones. It often works with a few tries.
2. Download the most recent version of Skype.
3. Dial in with your telephone or cell phone.

There are more answers on TalkShoe’s Help here