Cannot read property of Null

I keep getting an error message when I try and use Test battle
I uploaded a screenshot , It's weird because it keeps happening but then after a about 6 or 7 tries it works again , also battles work 100% fine in the actual game itself , it's only test battle that it keeps happening with.

Is there a way to find out what the problem is ?

There is a way to find out what the problem is, would be weird if there wasn't. Press f8 and show us the screenshot of the console log. Also it's good to show a screenshot of your plugins, they might be in a bad order for example. If it's crashjng in an event, it's not a bad idea to show the event code as well. If not, then that process can be skipped.

Without these screenshots it's really hard to help you with the debugging, sinde there are countless ways the very same error can be caused.

if sometimes it works and sometimes it doesn't, that means the object holding the property width is sometimes defined and sometimes not.
that can only happen as a result of randomization.
given that the only things that can have .width are sprites, bitmaps and windows,..... do you happen to have a background randomizer, maybe?

It doesn't have to be just ramdomizer, it can also be stuff not loading in time.

Some plugins work in-game but not in test battles or test events, because they set up their variables as part of the "normal" database loading process, and test battles and test events use a different loading process.

Does the problem happen straight away, before you even see the battle screen? Or does it crash partway through battles?

It happens while it's trying to load ,before it loads up the screen.
But right now it's working as normal so I can't show you anything lol , If I get it again tomorrow I'll be sure to press f8 and so you guys the report.

here is a screenshot of all the plugins many are OFF atm

Is it dependent on what troop you're trying to battle test, perhaps?

First question: Why do you have duplicate plugins? Both are also ON
I suggest you to look at your plugin list and remove all the duplicates.
I could see that you have 2 Core Engines, 2 Battle Engine Cores and 2 Super Tools Engines.

Additionally, the order of plugins is important, and your yanfly plugins are not only containing doubles but are also in the wrong order. They have to be in the order given on yanflys website - you can mix other plugins between them if neccessary, but you have to keep their order.

Sorry for late reply , I have edited and deleted the doubles of the plugins but I noticed today now , none of my NOTES are loading for example when testing a battle and the player uses their attack the camera normally zooms in but now it does nothing.....I swear these plugins are testing me.

then show us what you have now in your plugin manager

Some plugins only work when you do a normal play or test play - not in battle test or event test.

See if they work when you start a new game via test play.