This was the original "steps to reproduce" that worked "way back" (sometime in 2014) and now throws an error. Since the wiki says getVariable against a Task object can't take an array, I've changed the report but wanted to leave this in case it is helpful.
testTask = player createSimpletask ["Test Task"];
testTask setVariable ["TestValue",1];
testTask getVariable ["TestValue",0];
Throws at getVariable
Error Generic error in expression