I had the same problem, when I used the 4.2 linux version of the Skype client. It seems that it was a protocol mismatch between the Windows and Linux versions o

I had the same problem, when I used the 4.2 linux version of the Skype client. It seems that it was a protocol mismatch between the Windows and Linux versions of the Skype client, and the 4-digit number is the duration of the call in seconds.