I have noticed below problem and don't know how to fix it.
I have installed Issabel and registered some SIP lines after that I downloaded my current extensions in CSV format in System -> PBX -> Batch Configurations -> Batch of Extensions menu. Then I deleted my Issabel and reinstall it. In order to save some time to not register my old lines again, I wanted to use extensions.csv but I couldn't able to do it. When I try to upload CVS file or Download CSV format, the operation is failed. After I register 1 dummy SIP line, I could able to Upload/Download CSV file.