There are no restrictions on the trial version. Are you trying to import the same images again?
Which version of Lightroom are you using?
Which operating system are you using?
Could you please post the exact error message?
Please post a screenshot.
Which type if file are you trying to import?
no new files - und just to be sure I unchecked "don't import suspected duplicates
It seems you do not have appropriate permission in the destination location.
Please change the destination location and see if that helps.
You are trying to import to the Root directory of your Macintosh HD. I suspect that's not a good place to put your photos (but ... full disclosure ... I do not use MAC computers). You might want to set the Destination to somewhere appropriate under Users.
Or try to import using the ADD option.