You dont need the [harm] in the last bracket, just the [nomod], [mod:alt], etc...

basically if you have [] but don't specify nomod in it, then it will ALWAYS be true if that button is pressed, whether a mod is pressed or not.

So basically:

#showtooltip
/cast [target=focustarget, harm, nomod] [target=party1target, harm, nomod] [nomod] lightning bolt
/cast [target=focustarget, harm, mod:alt] [target=party1target, harm, mod:alt] [mod:alt] chain lightning
/cast [target=focustarget, help, nomod] [target=party1target, help, nomod] [nomod] lesser healing wave
/cast [target=focustarget, help, mod:alt] [target=party1target, help, mod:alt] [mod:alt] chain heal

Will work with error messages. You do have to add the harm, or help, if you want it to work without error messages.