I'd say odds are that you either didn't put the tip all the way in (in terms of depth) or that it's not making proper contact (try rotating it a little). For the record though, you should generally never go above 370C at the worst case scenario, as that could cause some damage to the board and/or component. Also, the temp probe that came with your meter is not intended to handle such high temps (I wouldn't trust it with more than 250C). For more accurate measurements, get the UT-T12 probe & the UT320D thermometer. Alternatively, you could get an FG-100 replica (which is directly intended for this purpose), this would be slightly less accurate than the first method, but still perfectly accceptable.