With the pagefile disabled the commit limit will be something less than RAM size. This can cause some serious problems, even when there is a great deal of available or even free memory available. It can also substantially reduce the amount of memory available. I would urge you to re-enable the pagefile to System Managed.
I have always hated that error dialog because it is so vague in meaning. "Low on memory" has multiple meanings and it doesn't tell you which one. A lack of RAM will reduce performance, possible seriously, but will rarely cause other problems. Hitting the commit limit will cause serious problems. But from the Task Manager numbers it is clear neither condition is true.
Out of memory errors are typically caused when the condition of a processes private address space causes a memory allocation to fail. But closing any number of other applications will have no effect on this situation.