Errors importing demo files

I have Highend WP Theme installed locally on my computer and am trying to install the demo files. I first I received two errors relating to maximum execution time and WP memory limit. I fixed both of those problems by editing the wp_config.php file. When I tried to import demo files (both with the 1-click importer and with the manual import method) I am getting error messages that the files failed to import:
(Warning: Invalid argument supplied for foreach()…)

I have tried resetting the database and retrying the process several times with no luck. Any suggestions? I’m about to give up and buy a new theme.