To check which records will not convert to float:
1. Import the spreadsheet with all columns as nvarchar(255).
2. Add a new float column to the table after populated
3. Update float column = Try_Cast(nvarchar column as float);
4. Select from table where float column is null, review the nvarchar column to see what values Excel imported. I bet it is a bunch of empty cells.
Good luck
Wes
(A solid design is always preferable to a creative workaround)