Windows 7: MagicDisc on w7 trouble

Hi i'm recently having a problem with magicdisc, which reads magiciso on my drop down list. Out of no where the drive that i usually mount iso's on no longer has a letter, and when i click change drive letter, i used to have it as L, i click ok and check it but it wont change. still just says ? where the drive letter should be. anyone have an idea on how to fix this, it literally happened overnight, i was mounting iso's last night.

Not an actual solution, but a reasonable work around - I had an identical problem, and I changed the number of drives ("Set Number of Drives") to 2. When you then go to Virtual CD/DVD-ROM, the drive assigned with a ? remains, but a new one has appeared which is useable. I just ignore the ? and use the other one. It seems to work fine.
Andy