When you install ExpandIT, Jet Reports will no longer work with a Navision Datasource. This occurs because ExpandIT renames the Fin.exe to Fin2.exe. To resolve this issue you have to explicitly specify the fin2.exe in your Navision Client Program Folder of the datasource setup.
Jet Reports v7 and earlier: Within Excel, go to Jet, Options, and select the datasource tab, in the option "Navision Client Program Folder", put in the complete path and filename of the fin2.exe file.
Jet Reports 2009 and later: On the Jet tab, click the "Data Source Settings" button, for the option "Dynamics NAV client folder" specify the complete path and filename of the fin2.exe file.
C:\program files\microsoft business solutions-navision\client\fin2.exe
This tells Jet Reports the exact copy of the fin.exe to look at.