Micro sd 4gb micro card.. i just bought a micro sd card with that adapter thing and took it home

Question

i just bought a micro sd card with that adapter thing and took it home excited to finally get music on my phone. and tried to open the removable disk. it comes up on my computer a removable disk D:\it would show the hour glass thing kinda freeze then an error notice would come up saying "D:\ is not accesible
the request could not be performed because of an i/o devise error."when i right click on the icon for the removable disk and find properties it shows that it can read how much space is on there. so it can read it.
so what does that mean?
bad card? bad port?
the port reads other memory cards....the 2gb card for the digital camera works fine in it. what to do?