This problem started on all 3 of my SRO PCs after the last client update a few weeks ago. 
All 3 PCs are using dual core processors. 
The only thing I've been able to do that actually helped was to go into Task Manager with SRO running (hit 
Ctrl-Shift-Esc) then go to the 
Processes tab, right click on 
sro_client.exe, choose 
Set Affinity. 

From the window that comes up, UNCHECK all 
except for CPU 0... leave CPU 0 checked. 
It has helped on all 3 of my machines, but I'm sure it's not a magic perfect fix. Good luck.