Please verify these:
1.Make sure to increase the file upload limit on your server. Contact your host for that.
2.Verify that MYSQL database has innodb support enabled.
3.Verify that your MYSQL server is not down, try restarting the server.
4.Make sure the csv file do not have any special characters non-UTF characters in the to be imported fields.If they have special characters, AEM will skip all such rows with special characters and import the rest.
5.If still issues, please send us an email to support(at)awebdesk.com with sample import file.