Hey Guest! Ever feel like entering a Game Jam, but the time limit is always too much pressure? We get it... You lead a hectic life and dedicating 3 whole days to make a game just doesn't work for you! So, why not enter the GMC SLOW JAM? Take your time! Kick back and make your game over 4 months! Interested? Then just click here!
Then you're using an old version and didn't specify so in the opening post. Not the best idea if you want to get responses tailored to your version. Also not the best idea to use old versions, as the last one that doesn't support that syntax is probably ancient by now.
OMG I forgot that was a GMS1.4 thing. I still kept thinking it was GMS2. Probably because I had been using GM8 for soooooo long. Or maybe this wasn't a feature in GMS1.3? I dunno.
...Did GM8 even have inline error detection? I thought it only spat out errors when you hit Play. (It's been a while since my laptop died.)
UPDATE: I did a quick google check. OP needs to update to GMS1.4.9999, since this was added in 1.4.1767