This can be caused by having a very large number of saved bank reconciliation reports in Reports > Bank Account Reports > Bank Reconciliation reports.

Take one of the following steps to resolve:

Unmark the checkbox for creating the reconciliation reports when reconciling.

OR

Delete as many saved reports as possible in Reports > Bank Account Reports > Bank Reconciliation reports. It's possible to pull up historical reports, so it's not necessary to have a different parameter for each reconciliation completed.