An unexpected error occurred (file 'named.app', line 388, function 'Renames::Normalizers') ??

I created a new column and wrote this expression :

Column 4 = CALCULATETABLE(tablename,IF(tablename[datecolumn].[Date]=TODAY(),MONTH(now())),IF(1=1,MONTH(NOW())-1))

It shows this the error:

An unexpected error occurred (file 'named.app', line 388, function 'Renames::Normalizers') ??

Any idea what was that?

why I wrote this expression:

I need current month name and previous month name, so I want to make both if conditions true.

Thanks for the time.