Backup plugins are not encouraged on Free hosting. They create excess load on servers. It is encouraged to backup and restore manually.
It can be because of once of the following reasons:
- File that you are uploading contains malware.
- File is larger in size than allowed limit. Different file types have different size limit. (.htaccess =< 10KB, PHP/HTML =< 1MB, Other files =< 10MB)
- File type is not allowed (e.g. apk, executable files including bat)