Upon running a report with an NP(Eval) formula, Jet Reports gives an error such as "Excel Could Not Evaluate..." and specifies the formula in the NP(Eval). The same error can happen in any function when tabbing between arguments in the Jfx or clicking the Jfx Evaluate button.
This error can be legitimately caused by the formula or argument not being a valid Excel formula. If the formula being evaluated is a valid Excel formula, this error may be a result of installing and then uninstalling a Multilingual User Interface (MUI) pack for Excel 2007.
In order to resolve this issue, you must do a repair of the Office 2007 installation. You can do this by going to Add or Remove Programs, finding the entry for Office 2007 and selecting change, then selecting Repair. Please note that this requires a reboot.