Regrettably, this is a known bug. You need to apply the hotfix. You can apply the latest one as the hotfixes are cumulative. Important thing here is that the Import toolkit is part of the setup files - not the actual web project. So, you need to apply the hotfix on the setup files. This can be done by going to the Advanced mode in this hotfix step and selecting to fix the Setup files. If you have already applied hotfix on the project and database, you can uncheck those options.