This error means that 2 or more eas are trying to open, close or modify their orders at the same time. There is one "stream" in metatrader for ea trading, so if one ea is busy talking to server, all the rest will have to wait until it finishes.

How to solve:
1. if you can code, just go to Error 146 ("Trade context busy") and How to Deal with It - MQL4 Articles, there is a description of this problem and functions to add to your code to avoid this happening in future.
2. If you cannot code, just use 1 ea per metatrader, or (if you want to run more than 1) make sure they will not trade too often. If you run 2 scalping eas at the same time, you will get quite a lot of errors 146.