Duplicate Tags (same except for upper/lower case)
If you have tags that are the same except for case, there's an easy way to fix this.
When we switched the tags to being case-sensitive in April of 2011, we also released DragonTagger, a bulk renaming tool. DragonTagger will allow you to rename your tags quickly so you can get them all to match and be the case you want.
To know more, you can read the original announcement