external sd - SD card problem, card gets suddenly removed and later added- Sony Xperia X8

I am using xperia x8 version 2.1 update 1.

Sometimes my phone creates problem with sd card i.e it automatically ejects stating "sd card unexpectedly removed" and after sometime it again shows "sd card preparing" and it works on. This distracts me to work in phone automatically the process gets delayed. I even tried by shutting down my phone, but the problem occurs.