I have also encountered similar problems when using MC26, and MC25, to rip discs even though my CD drive is internal.
If this is being caused by having any AV program other than Win Defender installed on "the PC where this problem occurs" I'd love to know why
MC26 - claims there is no Audio Files on the CD
Windows Explorer says there are Files on the CD
WMP12 - Not only says there are Audio Files on the CD it starts playing the 1st Track while doing a DB lookup to get the Tags etc
MediaMonkey - Also says there are Audio Files on the disk
Because I seriously doubt that AVG Internet Security is preventing MC from detecting that there are Audio Files/Tracks on a CD when it isn't preventing other programs from detecting that they are present.
But the problems I've encountered are not restricted to Ripping CD's because I've also encountered really weird things when Burning Tracks to a CD.
On more than one occasion MC has claimed there is No Disc in the Drive but lower down the screen it is informing me of the progress of the operation and the indicator lights on my CD drive are also telling me that MC is actually writing to the CD it is claiming isn't present
After MC has burned all the tracks to the CD I've also seen this message "Logical Unit Not Ready, Long Write In Progress" in the Burn Progress Window and when I look down at the disc indicator lights both the hard drive and CD drive lights keep flashing. However, if I leave the cd in the drive, cancel the burn operation and switch from MC to WMP12 - not only has WMP detected that there is a complete audio cd present it has found that disc in it's database.
You can do what I did and use Windows Media Player 12 to rip your discs to a different directory/folder to the ones MC uses and then Import them into MC so that you can add any additional info/tags.