I've found the source of error - mismatching of the parameter list with formula.
Actually I didn't find how to edit parameter list: once parameter is entered, it cannot be deleted.
For example in the example below I want to remove d parameter.
Just suppressing d in the cell doesn't help ... cell remans "activated" (i.e. bright color).
How to proceed ?
Here is solution: select the element to remove, right-click and from the context menu : Data Operations --> Delete Element.