Is that Windows would normally require read access (to check permissions and available space and the like) before it is able to write to a device.
Soooooo, with that in mind, what happens if you add "explorer.exe" (without the quotes) to the "Do not apply this rule to the following processes:" field? This is found in the rule properties, not the condition properties.
Doing this should give Windows the info it needs to be able to write to a drive, while still blocking other processes (e.g. winword.exe, cmd.exe) from reading from the drive. The problem is that with this exception in place, users would be able to copy from a removable drive. Is that acceptable? What is it you want to accomplish?
BTW, you've posted this thread in the Encryption forums instead of the SEP forums.