I recently heard from Gordon Portanier (from the Crystalize consulting group in Canada). He was doing something I have seen several customer do over the years. He would start certain formula names with a symbol so those formulas would sort to the top of the field explorer list. Gordon happened to use the @ symbol.

When he upgraded to CR 2020 these reports ran fine, but he found that he could not create a new formula that had an @ symbol in the name. A message told him that four characters [ @ { } ? ] were now considered reserved characters and could no longer be used anywhere within the name of a formula field.

Existing formulas, however, are not affected unless you try to rename them. So Gordon found another report that had the formula names he needed and copied them to the current report. The formulas work fine.

Up through CRv12(CR 2008) a formula name could include ANY character in any position. But when I tested this in CRv14.2 (CR 2016) I got the same warning as Gordon. My guess is that this restriction started with CRv14 (CR 2011) and so it would also affect CRv14.1 (CR 2103) and all later versions.  If any of you are using CRv14 (CR 2011) or CRv14.1 (CR 2103) you can confirm this by trying to add a formula with an @ in the name.  Let me know what happens.

An interesting point. This rule only applies to formula names. It does not affect the names of SQL expressions, parameters or running totals.

Another interesting point is that the @ (which represents formulas) and the ? ( which represents parameters) are reserved. But you can still use the % symbol (which represents SQL Expressions) and also the # (which represents running totals).