Got message say number of columns exceeded
The number of columns per sheet is 1024.
There is a new experimental feature tuning it up to 16000. I would suggest to not use it. Huge spreadsheets are a mess anyway. Keep it reasonable.
@Fruish, This could happen if you paste a complete spreadsheet from Excel. Try to copy only the columns with content.
Unprotect sheet(s) first. The protection extends to the limits of Excel which exceeds the number of columns in Calc. Cheers, Al