Strange, similar issue was reported here.
What version are you using (File - Help - About)?
Mine is Version: 2.46.4732.461 64-bit (May 2017), but there is a newer version already.
Ah, the same reporter... why didn't you continue with your previous topic, as it is the same issue?
Or maybe you tried to, byt raised a new topic by mistake.
Please try "=[Content]" to create a custom column, and check if it works fine.
Excel.Workbook() function, returns a table representing sheets in the given excel workbook. I am not clear your purpose of using it. It returns a error message: The formula is incomplete. Only there is no syntax errors, the "OK" is enabling.
Could you please share more details for further analysis?