Xsserver is Stupid. There I said it. lol I used them, hated them, and fired them. However in the process I had a similar experience. Just out of the clear blue, all as well and bam, scrapebox gave the same error your getting.
XS just decided to mess with their routers or something and started blocking the primary activation server for scrapebox or messing with the data. Be it from faulty equipment or ignorance I don't know. If you do a help >> test server connection are the lights for the secondary server all green and you get 1 or more red lights on the primary server? Thats what happend to me.
I forced scrapebox to authenticate from the 2ndary server. Go to your scrapebox folder >> configuration >> scrapebox.ini
Find this line
ServerReverse=0
change it to
ServerReverse=1
Then go to settings >> Select Download Server
and choose server #2.
This isn't the ideal setup for reasons which I won't go into, but it worked. Most likely if you do a Test server connection in a few days you will see all 6 green lights. At which point it would be advisable to change back to download server 1 and change your ini file back to
ServerReverse=0
It took them 3-4 days before mine just started working again as randomly as it had quit.
Although yours could be a different issue of course, but its got all the symptoms of what happened to me.