Put 'noop' in front of $tip, it's attempting to execute a command from $tip, since $tip succeeded, it returned 1 (meaning $true), so noop would prevent it from trying to do that, thus getting rid of the error message. 'noop' basically means don't execute what comes after as a command, just evaluate the identifiers and/or variables after it. The identifier might execute commands, but what ever it returns won't be executed.
I'd probably do a check for $active (the active window), and match it to both $chan and $nick (if $active is equal to either, it's the active window), also $appactive to see if mIRC is the active window, so I'd include a check for that. This would prevent tips showing when you are in the window where the highlighted message appeared.
on *:TEXT:*:#:{
if (($active == $chan) || ($active == $nick)) { return }
if ($appactive) { return }
if (Bank isin $1-) || ($me isin $1-) {
if $highlight(1) || $highlight(2) {
noop $tip(TipName,Highlight $network,$chan : $nick messages,$null,$readini($mircini,files,trayicon),$null,window -a $chan,$null)
}
}
}
