Is this all that was shown? What you’ve shared here is what’s called a “stack trace”, not an error message.
A stack trace shows you where the code crash occurred, which is very useful in figuring out why it broke. But a stack trace itself doesn’t tell what exactly broke.
Was there an actual error message you should share?
If you’ve already spend hundreds of dollars on forum software, maybe consider spending a few dollars on hosting too? Invision Community is large, complex software which needs beefy hosting to run well.
Running heavy software like this on free hosting is like buying a racing track without having a car. Sure, it has many fun corners and fast straights, but you won’t be able to enjoy any of them yourself.