script to check status in logfile

Hello friends,
Hope someone can help me to write a script shell:
I have a log file with data
Name server1 down 00:10:00
Name server1 up 00:20:00
Name server2 down 00:12:00
Name server2 up 00:22:00
Name server1 down 00:23:00 ( i ve down without up so error )
Name server3 down 00:11:00
Name server3 up 00:23:00
For each name of the server I must to check if after down I have up . if one is down with out up I have to put it in the error file.
thks
george