I want to block a number on 3com NBX100

In Nokia Lumia you can add contacts to block number thereby blocking incoming calls from them.

Goto to Menu>Settings>Call settings>call baring. In this menu select incoming calls and add that number.

Default Password is 0000 or 00000000 or Reboot into previous version and change password to an alphanumeric password The word "administrator" has to be entered as the User Name. this pdf could help (http://support.3com.com/infodeli/tools/nbx/50/docs/admin_nbx50.pdf) and this pdf will tell you how to update the machine to a newer version or if it is in the newest version you must downgrade it just folow the instructions on this pdf (http://support.3com.com/infodeli/tools/nbx/60/upgr_nbx60.pdf) or you could try and Connect a PC to the console port of the NBX (9600 baud, 8 data bits, 1 stop bit, no parity)1. All commands are case sensitive. At the NBX or SS3 Prompt type nbxDb. NBXs response- DBITEST (? for help):
2. At the DBITEST prompt type X.NBXs response-encrypted admin pass ---> (!Ofm0uealStEsrx1) 3. Contact 3Com Tech Support to have the password decrypted. if you have anymore problems i would be happy to help and if you cant fix it still i would be happy to do it for you for a small fee ..i hope this helped and i look forward to hearing from you

What software version are you running? Specifically 5.0.x and below or 6.0.x and above? Assuming you have plugged in the new phone and have discovered it on the system... If you know how to get to the users tab for either version, then select the users extn (example ext.100) and click modify(5.0) or on the extn number (6.0). Then scroll down in the section on the right where it says telephone list (5.0) or associated telephone (6.0) and select the newly added phone (example ext. 101). Once you select the new extn (101) and click ok or apply, you will have moved their user profile to the new phone. All of their recordings, passwords and voicemails will move with the profile.

"Call barring" isn't possible from your phone, it can only be access/set from the Network operator, if you really have problem, please call the customer care of your network operator, tell them your problem, they'll provide you the call barring code and will instruct you how to set it.
Good luck.
Thanks for using FixYa.

That needs to be done at the carrier level (AT&T, Verizon etc...). With a PRI you can do a little bit of routing the numbers you want to block to an bad destination but it isn't easy for most people to do as you need to be comfortable with the dial plan.

earlier this was possible.here r some codes just try them,
to activate NO ANSWER : **61*NUMBER*13#
to cancel #61*NUMBER*13#

to activate NOT REACHABLE: **62*NUM*13#

and some networks like vodafone already have these features. i dont know about other networks. if u use vodafone u can call the custumer care n they will do it.

Call 8008763266. Also check 3Com Primus Knowledgebase for savecore procedure.then check nboss.log.

3Com NBX Support Team

Sounds like they are daisy chained together and this glicth locked the system.  How are the switches routed through your network.  Do you connect via T1 or Fiber?