Why does my formula work in Excel 2013 but not-work in SharePoint 2013?

I have asked this more than once on SharePoint 2013 forums with no good answers...

...so I am hoping the Excel gurus might have some insight...

...please...

Why does my formula work in Excel 2013 but not-work in SharePoint 2013?

Why does this formula...

=IF([Request Type]="Review",(IF(ISBLANK([Request Date]),FALSE,TRUE)),TRUE)...work in Excel but fail when used it in SharePoint?

The intent of this formula is the following...

If the field "Request Type" has the value "Review" and the field "Request Data" is blank then show FALSE, otherwise show TRUE.

SharePoint saves the formula, but when a list item is saved where the formula is implemented, (under List Settings, List Validation), SharePoint does not say anything other than "List data validation failed" and that is it.

(I should mention that, for some yet unknown reason, I do not have access to be able to lookup the CorrelationID on this machine, but that's another long and sad story.)

(I should mention that this list is a custom Content Type, so may be that matters?)

Can you help?

Thanks.

Mark Kamoski.