All of the sudden, the Gate to the Strip requires a key and I have been in and out multiple times after passing the credit check. Is the a bug and os their a way to fix it?

It's a bug. I'm sure there's threads about it in the bug section.

if your on the pc press ~, click the door and type "unlock", press enter

Or you can kill one of the robots and then loot the body. The body contains the key to the entrance.

Wow you must of really pissed Mr House off for him to change the locks like that, he will be asking for his CD,s back next.