I was having the same issue even though I was 100% positive my login credentials were correct. I looked into the plugin code and couldn’t figure out what was wrong, but I came up with a workaround. The following is not an ideal solution but it worked for me.
Line 685 of the plugin is:
code = data;
Add the following line directly below that line:
code = '200';
This is telling the plugin to ignore the status returned from the request on the credentials and proceed with the import no matter what. Not an ideal (or good) solution but it worked for me. YMMV.
