Still an issue in LR2.7 runing on win7-64bit
Added an identity plate and get the following "error B4" written backwards and upside down
Open the folder where your image is located, then drag it to the box in the Lightroom identity plate setup. It works for me.
I tried drag and drop before.
In trying again, made the image smaller then the max high and it works now. (note: it's been awhile since I tried this, so the machine has had several updates to the OS and several reboots, so there is a possibility of something else, like a bad driver, getting fixed that resolved this issue)