Duplicate name exists on the network

If you have received the above said system message pop up in more than one computer.Then check your event viewer.If you found below mentioned error.

"The name "name :0" could not be registered on the Interface with IP address 192.168.**.40. The machine with the IP address 192.168.**.44 did not allow the name to be claimed by this machine"

Check your device with ip address 192.168.**.44.Its name may be same as your workgroup name.Change this name . It will solve your problem

Mail blockers

You may receive these errors in your mail blog .
Sorbs.net
216.93.169.80 does not like recipient.
Remote host said: 550 5.1.7 203.**.**.*3 is Currently Sending Spam See: http://www.sorbs.net/lookup.shtml?203.**.**.*3
 
Secureserver.net
Giving up on 216.*.*.*.

to=<***.com>, relay=mailstore1.secureserver.net[*.*.238.*]:25, delay=46738, delays=46735/0.04/3.3/0, dsn=4.0.0, status=deferred (host mailstore[*.*.*.*] refused to talk to me: 554-p3pismtp01-029.prod.phx3.secureserver.net 554 Your access to this mail system has been rejected due to spam or virus content. If you believe that this failure is in error, please submit an unblock request at http://unblock.secureserver.net)

mail-abuse.com

Jul 18 04:24:12 *** postfix/smtp[23437]: 48E3629802B: to=<*be@**as.com>, relay=mail1.**.

com[**.**.**.181]:25, delay=63461, delays=63461/0.04/0.46/0, dsn=4.0.0, status=deferred  refused 

to talk to me: 550 Service unavailable; Client host [*.*.*.*] blocked using Trend Micro RBL+.Please 

see http://www.mail-abuse.com/cgi-bin/lookup?ip_address=*.*.*.* )

barracudacentral.org

There are a number of reasons your IP address may have been listed ,including:

1. The email server at this IP address contains a virus and has been sending out spam
2. The email server at this IP address may be configured incorrectly
3. The PC at this IP address may be infected with a virus or botnet software program
4. An individual in the organization at this IP address may have a PC infected with a virus 

or botnet program
5. This IP address may be a dynamic IP address which was previously utilized by a 

known spammer
6. The marketing department of a company at this IP address may be 
sending out bulk emails that do not comply with the CAN-SPAM Act 
7. This IP address may have a insecure wireless network attached to it 
which could allow unknown users to use it's network connection to send 
out bulk email
8. In some rare cases, your recipients'  Spam Firewall may be misconfigured 

Run more than one biometric sensors based applications in a single system

If you want to run more than one  application with more than one biometric sensors  (Digital persona) in a single computer . You need to bind the application with their respective sensors.For this you need to install VDI in (Virtual box) that computer and install guest operating systems on that VDI.Now using USB filter option you can bind each and every USB based biometric sensor with a single  guest OS. Now you can run application from each guest operation systems (Windows or Linux) with USB based biometric support.

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Listener Not responding

If you lost contact with listener.Try to reload listener from lsnrctl utility.If it doesn't respond. Try to stop it .Still problem persist.

Find the process no of the listener.
# su root

# netstat -tvlnp | grep 1521

  (here 1521 is the port no of tnslsnr)
It will give you the process no

# kill -9 {processno}

  Kill the listener.

Then start the listener.

# su oracle
# . oraenv
#  lsnrctl start 

Still problem persists try once again form the netstat listing.   
   
It may solve your problem

DHCP Server MAC address based filtering

http://blogs.technet.com/b/teamdhcp/archive/2007/10/03/dhcp-server-callout-dll-for-mac-address-based-filtering.aspx

Refer this link for complete details.