I wrote the medchg.sys driver and it is extraordinarily stable -- it has not had any modification to the driver since May of 2006. Therefore, this is very likely to be a fault in the VMware virtualization code (it is not common to virtualize a tape library, so this is probably not well tested). I would recommend that you connect that same library/driver to a physical machine and see if the issue can be duplicated. If it cannot, it indicates that the problem lies with VMware. The blue-screen dump might give more information as to the cause, so if you'd like us to investigate further please contact us at firstname.lastname@example.org
and we can make arrangements to receive the dump file for analysis (please set the system to create a "kernel memory only" dump).