Get rid of SL_Id the first column.
Since you deleted your locations that sl_id does not exist.
Read here about the use and purpose for sl_id,
It is used for import duplicates, it is a specific id assigned when locations are loaded.
also the correct formats for csv file headers
Also refer to troubleshooting import if after you fix your files you still have issues you need to look at your WP config (assume it wasnt just one location you are trying to upload)
For anything else, we need to know your WP Plugin environment and the url where you are using SLP, I do not know if you have current versions or not. See Posting guidelines