pathauto is not working for some keywords

We are facing problem in posting posts and opening any webpage which ends with few particular keywords.

1. cannot post any content which contains keywords like varchar, varchar2, traceroute, etc
2. cannot see the previous posted pages which ends with the keyword perl
ex: http://www.aliencoders.com/content/displaying-file-contents-using-hash-perl
but http://www.aliencoders.com/node/279 will open the same page coz no perl keyword in the url
3. I cannot open even perl forum category , rest are opening. check in http://www.aliencoders.com/forum links (except perl all links are working fine)