How to use flashdrive on a Mac book Pro in the parallels partition

When you remove the flash drive are you ejecting it or just unplugging it? If the latter then you need to use the system eject to remove it. You must also eject it properly from within Windows.

It would help if you provided the version of OS X you are using in your configuration as well as more info on the hardware model and configuration. This information helps us know about your setup in order to provide assistance.

Also, what version of Parallels are you using? Do you have USB support turned on in Parallels configuration? Have you searched the Parallels forum for possible solutions or posted your problem on their forum? This should be your first place to look for help, not the Apple Discussions.

Make sure the flash drive is formated properly MS-DOS File System (FAT32). You then launch Parallels but don't start the virtual machine. From the Edit menu select Virtual Machine. Then add a USB controller. Select Connect to Macintosh. Then start the virtual machine. Window should now detect the new hardware and set it up properly. You can then access the flash drive.

Also check that you have USB enabled in the Parallels Configuration Editor, and set Connection Options to 'Ask me what to do' in the same panel.