There is a case of Debian when after installing it via pen drive made by unetbootin (or may be any other usb iso creater), it works fine with a full desktop environment except for one thing,
"the pen drive/removable drive doesn't mount with read/write or just incorrectly"
For this just edit your /etc/fstab file and find line starting from something /dev/sdx1 where sdx is going to be your pen drive and comment it out e.g. if I have only one hard disk then it would be /dev/sda,...
