Error "You are trying to open a QB file. Only QB company files can be opened this way", when trying to export an IIF file

SUMMARY:
An error shows up when trying to export the IIF(For QuickBooks) file from Web TimeSheet
The error is as shown below.
 
Problem: You are trying to open a QB file. Only QB company files can be opened this way. 
Solution: 1. Determine the type of file you are opening by right click the file and choosing Properties. The file type is listed under "Type of File" 
 
CAUSE:
This usually occurs when the file association of the .iif file is changed to other applications other than MS Excel.
 
RESOLUTION:
Change the file association of .iif file to open with MS Excel.