Make sure that recorder is allowed to access Skype API.
- Open Skype client
- Click Tools in the upper menu
- Choose Options
- In the new window click Advanced tab on the right bottom
- Click Manage other programs' access to Skype in the bottom
- Locate  MP3SkypeRecorder.exe in the list, click it to select and click Change button on the right
- Click Allow the program to use Skype
- Click OK and click Save to save changes