I know my computer tells me that sometimes, what are you using to plug the microSD into the computer? are you using the USB reader that comes with the acekard or are you using a MicroSD->SD adapter? If you are using the adapter then are you using an internal or external card reader?
I never used to have problems with an internal card reader but I got a new computer and forgot to get an internal reader for it so I just bought a cheap external one, now most of the time when I plug in the card it comes up and says it needs to be formatted, after some unpluggingand replugging, of the card and the card reader it ends up working, sometimes I need to restart the computer too.