This occurs if the VT Function Library add-in is not enabled. To enable the add-in, tick the VT Function Library check box in the Add-Ins dialog. You may also need to close and restart Excel. See Installation instructions.
It can also occur if you have referred in a formula to a defined name that does not exist or has been deleted.
If the problem persists, try the following:
•You should check that there is only one copy of the file VTLIB.XLA on your PC. The file should be in the Library sub-folder of whichever folder Excel is in (normally C:\Program Files(x86)\Microsoft Office\root\OfficeXX)
•Choose the Edit|Links command (click the Edit Links button in the Queries and Connections group on the Data tab in Excel). VT workbooks should have a single link to VTLIB.XLA