Not Bug Can't NPC items

I keep getting this error message when I try to NPC items. I've tried selling my items more slowly, ccing, dropping/picking them up again, and restarting the game. Any idea on how to fix this? Also: for some reason I can occasionally sell ETC items, but not for long? The problem doesn't seem to be consistent for me. I've attached a picture of the error I'm getting.

 

You have max mesos, try going to the fm to purchase billion coins from Albert to free up some space

 

OMG i had no idea that existed.... thanks so much!