It is because your character is classified as a naga. If you change your character's leg shape to something that is not a taur or naga, you should be able to gain access.
I've made an edit for the next release that should hopefully make this clear. If your character has visited the AccuPitch Labs before and the character's body has changed since, there will be a disabled button with a tooltip explaining why you can't re-enter. If you use the goo shifting menu on the same tile, you may need to move off the tile and return to it so the button will refresh--the update should hopefully fix this issue as well.