SQL Server allows you to limit the maximum memory that can be utilized by its Database Engine. You can use this feature in order to allow the OS to have access to memory that cannot be used by SQL Server and thus ensure stability. However you have to remember to re-evaluate this setting in the event of a memory upgrade on the machine.
You can perform the above action as follows:
Right click on instance name in SSMS - Select "Properties" - Select the "Memory" tab. You then get the below dialog (in this example I have set as maximum server memory 3GB):
The above method is a way to ensure OS stability by not allowing SQL Server to consume all memory in any case and by leaving an amount of memory available for the OS.
Now, in the case you get the "There is insufficient system memory in resource pool 'internal' to run this query." error you can try the following actions:
Action 1
Run the T-SQL command:
ALTER RESOURCE GOVERNOR RESET STATISTICS
As described on an MSDN Library article, the above command will cause Resource Governor to resets statistics on all workload groups and resource pools including the "internal" resource pool.
Action 2:
If the above action does not solve the issue you can try to free-up more memory and eventually upgrade the memory capacity of the machine.