well boys and girls, mr wizard found 1 solution to the problem. i changed the application pool to use .net 4. not sure if dnn 6.x supports .net 4 but that solved the immediate problem.

if you do not have the option to use 4, you may come across advice suggesting use of   "<trust level="Full"/>" in either the web.config or machine.config files, none of which worked for me.....

you will come across a lot of pompous asses telling you to follow the advice of the error message. unfortunately it didn't help me.

this security problem is interesting because i have done at least 1 6.x upgrade using .net 2 for the app pool.