When you submit an HTC unlock, first thing we do is check whether a code is available for you
So if you have the IMEI is invalid message, or 'Please Check the items marked in RED', you should also see the following text
The following IMEIs have failed:
XXXXXXXXXXXXXXX No Service/Code available for this IMEI
This isn’t an error this is just informing you immediately that we will be unable to generate a code for this phone