I had a v4 application. The author made a v5 version. The instructions were to install the v5 as a new app, and then import the data.

That worked great.

Then I was looking at other applications to see if there were updates and saw first my current application, then one that said something like not currently installed (I can't see it now - the site is down), then a third set that said something like out of date.

The one in the middle (not installed) listed the old version of the app I just installed, so I clicked the X next to it and now I cannot access my site or my ACP.

Please advise, or help

@Daniel F

Please try recovery mode as shown here

https://invisioncommunity.com/4guides/client-services/getting-support-r292/

If that doenst work, please check what error is being shown in your server error logs

Resolved by app author, thanks.