User is comparing the balance of the 3900 - Retained Earnings account (by using the View Report option for this account) and the Balance Sheet Cash Basis report. The values do not match.
This is by design in CORE. The Retained Earnings account report shows the full billed value of the invoices, but the Balance Sheet Cash Basis report only shows the value of the payments made as of the date used to run it. These are not expected to match as they are reporting on totally different criteria. Also, the 3900 - Retained Earnings account does not show a balance on the Chart of Accounts screen and so you cannot drill down on this account on the Balance Sheet Cash Basis report. This is because the Retained Earnings account does not actually have any transactions against it. It is essentially a derived or calculated value, and not based on actual transactions. The balance in the Retained Earnings account report displays the income of previous years as well as the current year, but the balance sheet report displays only the last year's income. You might want to check out this article: Retained Earnings in CORE.