Expected numeric/value expression

Hi experts,

I'm new in VC and have very strange problem:

When I'm trying to format fields or write IF expression, I'm getting an error "<b>Expected numeric/value expression"</b>.

For example, NSTR(@value,"9.2")  or IF((ISNULL(@value1),@value2,@value3).

What is the problem?

Thanks in advance,

Inna

P.S.

We have EP7 SP11 and I'm trying to edit fields in <b>charts series</b>.