I've read over most of this thread and have found that some people are having luck with reformatting, and others need to buy new cards altogether.
Formatting never solved my problem so I bought a new 4gb Class 4 Kington Micro SD card and have never had an issue. Some info that I gained from reading various different forums and bug reports on the issue (with other Android devices[LG Ally in specific, but others as well]) have come to the conclusion that Class 2 SD cards have a tendency to cause problems, and that Sandisk and Samsung cards also tend to have issues. This is all from a personal standpoint, and the formatting fix may solve your problem, this is just an alternate to try if you have not had luck formatting.
Formatting never solved my problem so I bought a new 4gb Class 4 Kington Micro SD card and have never had an issue. Some info that I gained from reading various different forums and bug reports on the issue (with other Android devices[LG Ally in specific, but others as well]) have come to the conclusion that Class 2 SD cards have a tendency to cause problems, and that Sandisk and Samsung cards also tend to have issues. This is all from a personal standpoint, and the formatting fix may solve your problem, this is just an alternate to try if you have not had luck formatting.