Slow Response

Has anyone experienced slow response rates, especially refresh rates, when using Navision as a standalone product? We have a customer with 4 sites across the country using Navision Financials Software 1987/99 version W1 2.50. Three of the sites are working fine but the other one has had slow response issues since day one. The sites and application became operation about a year ago. However, when they use Navision with the Citrix client it operates with no problem. At least one other site say they use Navision without the Citrix client.