When trying to connect your local disk (CD/DVD) drive to a VM in vSphere Client, you can get the following error message:
Remote device connection
Could not open the client device “DriveLetter:”. It is being used by another virtual machine or some other program.
This is caused by the device being used by another virtual machine or by modifications to your operating systems usage of the local CD/DVD device (hence the some other program part of the error).
To fix this you can either change the way your other program manages the CD/DVD device or in the vSphere Client, open a console view to the VM, click VM -> Edit Settings… -> Select CD/DVD drive -> then under Mode, select Emulate IDE. You should now be able to connect to your local disk without the Could not open the client device error.
Note that my research on the internet showed that running the VMware vSphere Client as an Administrator fixed this error for some people.