As long as you aren't exceeding the number of licences allowed you should be OK but of course the account doesn't know when you uninstall from one machine and then try for another so it may be necessary to speak with Customer Service to get it sorted.
Click McAfee Support at top of this page > Home and Home Office Support > Customer Service. There you should have the option to either speak by phone or chat online, both are free although with the phone some long distance charges may apply depending on where you are. Email isn't recommended as it takes forever. They are only open Monday to Friday in the UK.
Thank you for the quick reply. Looks like i'll have to wait until monday
Wont it let you install?