[Plugin: Search and Replace] warning message

hi i’ve a buddypress community, i just moved it from a host to another one, i need to replace some stuff (like forum topic, documents uploaded) that still redirect to the same files in my old site.
The support of my new host told me to use this plugin, but when i do the search, i can see all the results but i also get this message:
Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in /home/sartoria/public_html/wp-content/plugins/search-and-replace/search-and-replace.php on line 917

i dont know if i can use this plugin… if i can u explain to me better where i have to put the old host name and the new one ?
thank u

https://www.ads-software.com/extend/plugins/search-and-replace/