Grid antenna problem

hi guys, iam sorry if this is the wrong place to ask but i had 2..anyway 3 months ago i installed atheros5700g card with 10 dbi omni antenna which worked great and i was able to connect to open networks near by me, so i decided to get
a better antenna to access more net works so i got grid antenna 24dbi etc...
the thing is while it gets alot of networks it canot access those that i used to get with my omni antenna..i though my card went wrong or so so i returned my omni and bam it works fine ..only with my grid antenna i get the windows cannot connect to network problem?? iam using win 7 btw, Any advise please??

p.s sorry for my english its not my first language