same thing happened with me as well. i had 8 gb micro sd card that came up with the phone.
yesterday i used it to install windows 7 on my acer aspire one d250 netbook. after that i formatted it and inserted into phone, it said "memory card removed, insert new one" though the computer was able to read it.
i reformatted it with fat32 and again inserted into myphone, same result
again with ntfs and same result(using mini tool partition wizard)
today also i kept playing with my sd card
just a couple of minutes ago i formatted my sd card with fat32
and then i right clicked my sd card in mini tool partition wizard>>>>> then i clicked "modify">>>>>>then clicked on "change partition type id"
>>>>>> i changed it to "0*06 fat16,greater than 32 mb" >>>>>>>and then yes
and guess what now my phone can read my sd card
and don't forget to apply changes on the left hand side on mini tool partition wizard
hope it helps