Hi Eugene,
Thank you for your interest in Syncfusion Products.
To use the formula engine, there must be a FormulaTag object for each cell. In a non virtual grid, this is stored in the cell's GridStyleInfo object. But for a virtual grid, there is no GridStyleInfo object stored for each cell, hence the problem. One solution is to maintain a collection of FormulaTags for the cells that are formula cells.
Please refer the following sample for the implementation:
http://files.syncfusion.com/support/Grid.Windows/54786/main.htmPlease let me know if this helps.
Regards,
Jisha