I currently have a P1 one plan and I know you can't transfer one to the other.  Is the only way to do it is by cancelling the P1 sub and let it expire and then once expired start a E1 plan?

Hi,

You could start the E1 now, that way while both are running you move any stuff over that you need.

Sorry! We can't process your request right now.

The offer that you want is unavailable. This might be caused by one of the following reasons:

The offer has expired.

The service is not available in your country or region.

You cannot sign up for the same trial a second time.

Hi,

Not sure what is blocking you, or where you clicked to get that error, but I had both an E3 and P1 trial at the same time, so I know you can have more than 1. E1 plans however do seem to be available as a trial, so if you are sure you are headed that way, just click the buy now on Microsoft.com.

I did do the buy now.

That message is what you see when you reclick the OLSB 6 month trial offer. Presumably 365 "thinks" you're logged in and have already signed up for a trial. The sign out process MSFT uses doesn't work very well so you may have to close your browser and even clear your cache to ensure you're logged out of the id associated with OLSB.