Error – Unable to open file for reading

Hello,

When importing a file, the file loads successfully to 100% and presents the Preparing to Import screen. A few second later we get the “Unable to open file for reading” error.

What is the cause of this specific error?

Actions we have tried:
– Increasing the max upload size
– Increasing the max execution time
– Rolling back the version of the plugin
– Trying various backups – all fail, so the one in question is not corrupt

Also, the hosting provider is supported as this plugin works on numerous of our other sites.

Any advice would be appreciated.

Regards,