Check to be sure the destination folder is writeable, and that you have WRITE permission to the destination folder.
Its the internal hard drive in my iMac. I was able to write to the drive for the previous 300 photos imported 30 minutes earlier
Okay, if you're not going to check, that's up to you.
But that's what the message means, you don't have WRITE permission to the folder or the folder is set to read-only. Possibly, it could also happen because the Destination folder has (accidentally?) been changed to some place where the permissions are not WRITE permission.
I didn't mean to insult you,
Yes as You were responding I checked by right clicking over the My hard drive location in the right pane in library.
It did say read only under permissions. How would that have changed between imports? I want to be able to keep it from happening again. I am the only user
System, read and write
Wheel, read only
Everyone, read only
I don't know how these things change, but people report they do change.
It's not the permissions on the disk that are important, it's the permissions and read-only status of the Destination folder that are important.