Spreadsheet FALSELY says column limit of 256 has been reached

Spreadsheet FALSELY says column limit of 256 has been reached

I am trying to add a column to a simple ZOHO DOCS spreadsheet that currently only has data in column A-T. 
When I add 'insert column' the pop-up message tells me I have reached the 256 column limit. Clearly I have not.  I wonder if highlighting a whole row blue has caused this error??

I have attached a screen shot.\

When I delete the  'u'  'w' or 'v' columns, the problem does not resolve.

Can anyone advise a workaround?  Less than 24 columns is nothing to work with.

Thank you
LBB