Maximum Number of simultaneous devices connected to one client

Hey there,

is there a limitation for the maximum number of devices connected to one client at the same time?

I have a virtualhere server running on a raspberry pi b+. On each USB port of the pi there is a 4-port usb hub. One each port of this hub there is another 4-port usb hub. On this four hubs there are 15 usb to serial converters connected. All together ther are 60 usb to serial converters connected to the raspberry pi and 20 usb hubs.

The virtualhere client (Windows) shows me all 60 converters, but if i connect all of them to one client my windows shows only 16 in the device manager. The client software shows "In use by you" for all 60 devices. Whats wrong there?

Any ideas why?

Regards daice