The voxel mods are just that, a User Interface upgrade. So once you remove the voxel mods the save no longer appears in the save selection? That is strange. Can you post another console log with the voxel mods disabled for everyone to see?
My search through Google turns up a few possibilities. One is a corrupt save. The fix suggested for a corrupt save is to delete chunks with MCEdit until you find out which one is corrupted or start over. Be sure that if you try this to delete one chunk at a time until your save file opens up and then make another copy and try only deleting that chunk to see if it is only that chunk so you only loose that one chunk. The other possibility is that one of your mods is saved as a .jar.zip file instead of a .jar file. A force update might fix that as well. Other than that I'm pretty much out of ideas. Hopefully someone with more experience with corrupted saves will come by. Good luck.
A miss-write is what happens when your game tries to save its progress and it either does not completely save or it accidentally saves a bit wrong, say a 0 instead of a 1. This can cause minecraft to read the save as something other than a save or cause an error while trying to read it if it is in a critical part of the file.