AMI with USB Hard Drive Problem

[tc4332]

Help.
I am now suffering from the complexity of the A8.
Why can't it be really and completely plug and play.
I retro fitted an AMI and it worked really well once I realised that the storage device being used via USB must be formatted with Fat32. I have been using a 32GB SD card without problem.
I bought a used 230GB Audi hard drive on fleebay, formatted it with Fat 32 and it worked fine whilst testing it on the AMI when it had a few files recorded.
I went daft and saved quite a few files on the hard drive, fitted it in the car and it works spot on . . . . some of the time. When it does not work the message "device not connected properly" comes up. This happens when starting the car i.e. ignition switch on. The only way I can then get it to work is by unplugging the micro USB plug on the hard drive, wait a few minutes, plug it back in and away it goes. Then the thing works really well until the next time I start the car.
When it works it seems to take longer to "initialize" itself than the SD card did.
Has anyone else met this problem?