Error while exporting Requirements with blank test cases

Hi,

 I have Requirement in Cloumn A and its description in Column B and Test Case -Tile and Descriptions are in Column  E and Column F respectively of excel sheet.

Some of the Requirements have not any assocaited Test case Titles and description and it is blank cell.  I am getting the following  error for those while exporting using ExcelImporter Addin 4.0.1.

Error sending to server Book2_TCER_7.xml of type testcase

The remote server returned an error: (500) Internal Server Error.

However i can continue it after  this error dialog and my requirements  got esported properly.

How to correct this error or is there any way we can modify our CFG file to check before exporting the blank columns of test cases ?

Thanks-

Chandan