Thank you Alícia, my mistake!
The settings seem to be all right. Do you use any customizations, custom codes or anything related to Ajax Search Pro by any chance? I’m asking because even empty requests return an error, which usually happens when there is an issue with a customization.
If not, then can you please add temporary SFTP details? I will have to debug through the search process to see where it fails, there is probably an error message which will lead to the solution.