Accessed None means that the value that is trying to be set is not yet (or just isn’t) initialized/known by the node trying to use it. The error message should say which variable is not being set. It can also be that you are using a value that you have no initialization for.
If this happens at the very start of gameplay, it may indicate that it is too soon to attempt to use the variable involved.
By checking IsValid on the variable before attempting to use it, you can do something like a delay before proceeding so the value isn’t attempted until ready. If it is an initialization you haven’t allowed for, it will never be set and will need to be addressed.
Kind of a generic answer but, I can’t say anything specific without the complete error message, but you should be able to figure out which is failing to be set by the rest of the content of the message. Here is an example of one such message from my log:
Blueprint Runtime Error: “Accessed None trying to read property CharacterReference”. Node: Set Direction Graph: EventGraph Function: Execute Ubergraph My Anim Blueprint Blueprint: MyAnimBlueprint
This means that my variable Direction in MyAnimBlueprint is trying to be set with a invalid value due to CharacterReference not being set (e.g., null). In this particular case, it’s happening at startup because the value being used to set CharacterReference hasn’t been provided to the blueprint yet so it’s property called Direction can’t be used in the Set node. Each case will be different as to the solution, but you know where to look from the error message.