Insufficient system memory in resource pool

Hi,

When application guy press submit button, he is receiving this error:

There is insufficient system memory in resource pool 'internal' to run this query. A serer error occured on the current command. The results, if any, should be discarded.

I think this error is related to sql server (SQL Server 2008, SP3 64X running on windows 64 bits) not application. Total memory is 32GB. 4 GB assigned to other instance and 24GB to this instance.

Any help?

Thanks