Hi Adel,
for future purposes i would like to highlight "No Available Conference Bridge" is a standard error messages from CUCM error dictionary .
Below is the link for "Troubleshooting Guide for Cisco Unified Communications Manager" which clearly explains the error
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/trouble/8_6_1/trbl861/tbsrv.html#wp1047093
Link Summery:
No Available Conference Bridge
Symptom
The following message displays: No Conference Bridge Available.
Possible Cause
This could indicate either a software or a hardware problem.
Recommended Action
1. 
Check to see whether you have any available software or hardware conference bridge resources that are registered with Cisco Unified Communications Manager.
2. Use the Cisco Unified Communications Manager Cisco Unified Real-Time Monitoring Tool to check the number of Unicast AvailableConferences.
The Cisco IP Voice Media Streaming application performs the conference bridge function. One software installation of Cisco IP Voice Media Streaming will support 16 Unicast Available Conferences (three people/conference), as shown in the following trace.
Note The number of supported devices may vary with different Cisco Unified Communications Manager releases. Refer to the appropriate version of Cisco Unified Communications Manager documentation at the following location:
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_documentation_roadmaps_list.html
10:59:29.951 CCM CallManager|UnicastBridgeControl - wait_capabilities_StationCapRes - Device= CFB_kirribilli - Registered - ConfBridges= 16, Streams= 48, tcpHandle=4f12738
10:59:29.951 CCM CallManager|UnicastBridgeManager - UnicastBridgeRegistrationReq - Device Registration Complete for Name= Xoð ô%ð - DeviceType= 50, ResourcesAvailable= 16, deviceTblIndex= 0
One E1 port (WS-X6608-E1 card contains 8x E1 ports) provides five Unicast Available Conferences (max conference size = 6), as shown in the following trace.
11:14:05.390 CCM CallManager|UnicastBridgeControl - wait_capabilities_StationCapRes - Device= CFB00107B000FB0 - Registered - ConfBridges= 5, Streams= 16, tcpHandle=4f19d64
11:14:05.480 CCM CallManager|UnicastBridgeManager - UnicastBridgeRegistrationReq - Device Registration Complete for Name= Xoð ô%ð - DeviceType= 51, ResourcesAvailable= 5, deviceTblIndex= 0
The following hardware trace on the Cisco Catalyst 6000 8 Port Voice T1/E1 and Services Module indicates that the E1 port 4/1 in the card registered as a Conference Bridge with Cisco Unified Communications Manager.
greece-sup (enable) sh port 4/1
Port Name Status Vlan Duplex Speed Type
----- ------------------ ---------- ---------- ------ ----- ----------
4/1 enabled 1 full -Conf Bridge
Port DHCP MAC-Address IP-Address Subnet-Mask
-------- ------- ----------------- --------------- ---------------
4/1 disable 00-10-7b-00-0f-b0 10.200.72.31 255.255.255.0
Port Call-Manager(s) DHCP-Server TFTP-Server Gateway
-------- ----------------- --------------- --------------- -----------
4/1 10.200.72.25 - 10.200.72.25 -
Port DNS-Server(s) Domain
-------- ----------------- -------------------------------------------
4/1 - 0.0.0.0
Port CallManagerState DSP-Type
-------- ---------------- -------- 4/1 registered C549
Port NoiseRegen NonLinearProcessing
----- ---------- -------------------
4/1 disabled disabled
3. Check the maximum number of users that are configured in your ad hoc or meet-me conference to determine whether the problem occurred because this number was exceeded.
4. Check the setting of the Audio Bandwidth field on the Location Configuration window. If the call bandwidth exceeds this configured limit, the conferencing fails. To resolve this issue, choose the Unlimited Bandwidth radio button. For more information on the Location Configuration window, refer to the Cisco Unified Communications Manager Administration Guide.
HTH
JB
