How to enforce user to select more than one value for Select List (multiple choices)?

[Teja]

Hi

I am trying to validate multi select cf, 

based on these cases

if the 'Environment' contains "FTE" then
case1

else
case2

if case1 then 'Environment' must contain "FTE" and at least 1 value other than "FTE"

else if
case2
'Environment' must contain at least 1 value other than "FTE"

Here: Environment is multi select list cf and it has values in it "FTE", "AAA", "BBB", "CCC"

How can we achieve this using 'Custom script validator'?

Thanks

[Teja]

Found the solution.