WinCDEmu cannot mount more than only one ISO-Files from an external USB-Disk.
OS: Windows 7-32
But when I transfer the second ISO-File to a local Partition (not the same as OS) I do not have any problem to mount the second disk from local partition.
For information: With Windows 8 (I am running it from a VHD on the same machine) I do not have any problems to mount 3 or 4 (never tried more) from the external USB Drive