Fail to access one site

I could not figure why the system fail to access the A1 site from "Geocortex Essentials REST API"

 

and give me the error shown in the attached screenshots, while I can enter other sites like s1.

 

/customer/servlet/servlet.FileDownload?file=00P6000000em1iNEAQ

 

/customer/servlet/servlet.FileDownload?file=00P6000000elzYEEAY