Dimension value locked to one code by Value Posting
A default dimension on the record named in the message, here customer 10000, uses Value Posting = Same Code with a fixed value, so every line for that record must carry exactly that value. The line carries a different one, so Business Central refuses to post it. Set the dimension value on the line to the value named in the message, or have an administrator change the Value Posting rule on that default dimension if the restriction is out of date.
Each default dimension on a master record has a Value Posting field with four options: blank means anything is allowed, Code Mandatory means some value must be present, No Code means the dimension must stay empty, and Same Code means only the value stored in the default dimension is accepted. When Same Code is combined with a Dimension Value Code, that value becomes the only legal one for every document line touching the record. Newer Business Central versions state the conflict explicitly, naming the required value and the value currently on the line, where older NAV and Business Central builds only said "Select Dimension Value Code ... for the Dimension Code ...".
Use Same Code only where the value is truly invariant for that record, for instance a customer that must always be reported under one department, and prefer Code Mandatory with a default value everywhere else, because it still guarantees an entry without forbidding legitimate exceptions. When the fixed value changes, update the default dimension and the documents that are already open, since they were created under the previous rule. Where two records both impose a value, decide the winner once through Default Dimension Priorities rather than letting each user resolve the conflict by hand.
Code Mandatory means the dimension must have some value, any valid one. Same Code means it must have exactly the value stored in the default dimension. Same Code with an empty value means no value at all is accepted.
No. With Value Posting = Same Code and a fixed value, an empty dimension is refused just like a wrong one. The line must carry the value named in the message unless the rule itself is changed.