Aaron,
Verify that the Dynamics.set matches the instance that works and the instance that has the error. (Typically located at C:\Program Files (x86)\Microsoft Dynamics\GP2010). If it is a new install, the default location is usually set to C:\Program Files (x86)\Microsoft Dynamics\GP2010\Data. If you use a shared location you can either edit the Dynamics.set file in notepad or within GP on the workstation that needs to be updated by navigating to Dynamics GP > Tools > Setup > System > Edit Launch File - highlight Microsoft Dynamics GP in the top pane and then enter the proper address in the lower pane - only for the Reports.Dic and Forms.Dic
Other options can be found at support.microsoft.com/KB851052.
Hope that helps,
Claude