Okay, did some testing and found... the problem has to do with your spaces!
"Couldn't parse <whatever>" is what is said when you try to execute a command that doesnt exist.
/newif (1) && (1) /echo hi
Couldn't parse '&& (1) /echo hi'
/newif ((1) && (1)) /echo hi
[MQ2] hi
So if you're going to use spaces, you do need to use parentheses around the whole thing

We could require parentheses in /newif... hmm..
So it was actually a /newif (and the same thing would happen with /if actually) issue. But, I did find an issue with ! during my testing.
${Math.Calc[!0&&1]} => 0 (incorrect)
${Math.Calc[(!0)&&(1)]} => 1 (correct)