I finally had the time to try your proposal but it does not do the trick.
Still getting the same error 'We found a problem with this formula. Try clicking Insert Function on the Formulas tab to fix it.\n\nNot trying to type a formula? When the first character is an equal (=) or minus (-) sign, RadSpreadsheet thinks it is a formula. For example, when you type =1+1 the cell shows 2. '
In the screenshot you can see how the data looks like in the RadGrid. The problem is in the column 'Serial Number'. You see that the second row has a value beginning with minus (-).
I added the OnInfrastructureExporting="grdEnquiry_InfrastructureExporting to my grid and the code in the event :
protected void grdEnquiry_InfrastructureExporting(object sender, GridInfrastructureExportingEventArgs e)
var rows = e.ExportStructure.Tables.Rows;
var rowCount = rows.Count;
var desiredColumnIndex = 8;
for (int rowIndex = 1; rowIndex <= rowCount; rowIndex++)
rows[rowIndex].Cells[desiredColumnIndex, rowIndex].Format = "@";
but still the same message.