"WP-Property: Importer" Add-on is using PHRETS library for doing requests to RETS providers. The library uses cookie file for user-agent authentication, which is being stored in temp directory.
You have the issue with temp directory. There may be different reasons:
PHRETS library uses sys_get_temp_dir() function to get path to temp directory. So you can use the function to determine the path to your current temp directory.
You can find more details about the function here: http://php.net/manual/en/function.sys-get-temp-dir.php
If you are not able to resolve the issue with the current temp directory you can define the custom temp directory.
Custom temp directory can be set via
WPP_XMLI_COOKIE_DIR define. You just need to set it in your
define( 'WPP_XMLI_COOKIE_DIR', 'full/path/to/your/custom/temp/directory' );