Are you sure you've got the Canon ip4500 setting selected in the "Paper Type" setting? There's a different setting on the Print screen for your printer driver. When you look at your label design, does the setting below it look like this?
If it's still asking you to close the inner cover, with that setting, click Print in Acoustica CD/DVD Label Maker, then click Properties. These are the settings for your printer. Make sure it is set to print on CD/DVD there.