In this case, you may want to try to open WavePad, click on WavePad and click on Options > Audio > Audio working folder and confirm if you are using the default folder or if you are using a custom one. Copy the folder path and go to the folder on the computer you are using, Delete any information you have there to liberate space and once you have deleted all the files you no longer need you may close and reopen the program, and test again.