The VBA procedure `I_UnRegisterFunctions` withdraws the registration of the Excel formulas of Invantive Control for Excel with Microsoft Excel. There are no parameters. It is the counterpart of [[I_RegisterFunctions]] and runs when the add-in is de-activated. Called on its own it makes the formulas unknown to Microsoft Excel until they are registered again, which is why it is used only to re-register a broken integration rather than on its own.