It will tell you X is the maximum amount of space available, when X amount is actually too high. What I've found is Disk Management can be wrong about the maximum available space. One thing I would try is when it asks you to select the amount of space in MB to extend the volume, select an amount slightly less than it says is the maximum available. It also shouldn't matter how large or small the available unallocated space is. You should be able to extend any non-boot volume/partition(or, in theory, even any boot volume/partition not currently in use) on the same drive to encompass the unallocated space available. Especially since we're talking about an SSD. It should make no difference if that unallocated/free space is contiguous with any particular partition on the drive. In your case I can't understand why it wouldn't. Because they're are times when that doesn't work. Well.that's why the italicized ' should'.