Microsoft Navision C/Front is the interface that the Jet Excel add-in uses to communicate with Dynamics NAV 2009 R2 and earlier.
C/Front is part of the Navision SDK, and can be installed from the Navision Client CD from either the Devkit or SDK folder, depending on the version of Navision. One version of C/Front must be installed when using Jet Essentials with Dynamics NAV. The version of C/Front should match the version of the NAV Client installed (the version of the executables).
If you run multiple versions of the NAV Client, you should install only one version of C/Front.