C#npoi error cannot get a numeric value from a text cell resolution

This is usually due to the fact that the value in the cell is a number, and sometimes the text format does not solve the problem.  
The code below is C # changing the way the cell type  is set using this parameter celltype.string

Row.getcell ((int) customer_level_index). Setcelltype (celltype.string);
Detail.customer_level = Row.getcell ((int) customer_level_index). Stringcellvalue;

The bottom is online.

When the POI is actually Setcellvalue, the Celltype is automatically set according to the type                        of the incoming parameter, so long vll = long.valueof                                                      (Vls.trim ()); // Sheet.getrow (i). Getcell (j). Setcelltype (cell.cell_type_numeric);      Mark off, or there's an anomaly                            . Sheet.getrow (i). Getcell (j). Setcellvalue (VLL);

C#npoi error cannot get a numeric value from a text cell resolution