Finally
"Application pool 'DefaultAppPool' is being automatically disabled due to a series of failures in the process(es) serving that application pool."

First a lot (5) of:

"A process serving application pool 'DefaultAppPool' terminated unexpectedly. The process id was '3836'. The process exit code was '0xffffffff'."

I finially figured it out when I noticed by:

On an application pool - Right Click - All tasks - Save Configuration File

It created an xml file with the pool configuration.

I had noticed the web page would start if a different Application pool (MSSharePointAppPool on mine).
So I exported that too and compared using an excellent opensource file compare tool WinMerge.

Major differences were a couple of passwords for the same user ID, but that wasn't it.

Here's the section that needs to be replced:

THIS (BAD):

<IIsApplicationPool Location="/LM/W3SVC/AppPools/DefaultAppPool"
AppPoolAutoStart="FALSE"
RapidFailProtection="FALSE"
/>

WITH THIS (GOOD):

<IIsApplicationPool Location="/LM/W3SVC/AppPools/DefaultAppPool"
AppPoolAutoStart="TRUE"
AppPoolIdentityType="0"
DisallowOverlappingRotation="TRUE" MaxProcesses="1"
RapidFailProtection="FALSE" />

You've got to stop the Default site, go to properties - HomeDirectory - Application Pool - switch it to an unused name,
then delete the old DefaultPool, then right click Application Pools - New Application Pool (from file) -
Browse to your fixed xml file - Read File - Select the name (s/b DefaultServer) then OK button.
Right click, start your repaired default pool. Go back to Default Web Site, right click properties -
HomeDirectory - Application Pool - pick the now dixed DefaultAppPool - Restartserver.

It works! Wow, how did you do all that?

That's why they call you a technical person.

Now lets go back to our simple Vb.net problems.