Posting date outside the allowed posting range
Business Central refuses the entry because the posting date on that line falls outside the window of dates you are allowed to post in. The window comes from Allow Posting From and Allow Posting To, first on your own User Setup record and, when those are blank, on General Ledger Setup. Either move the posting date into the open window, or have an administrator widen it.
Before it creates any ledger entries, Business Central compares the posting date of every journal line and every document with a permitted posting window. It reads Allow Posting From and Allow Posting To on the User Setup record of the person posting; if that record does not exist, or both fields are blank, it falls back to the same two fields on General Ledger Setup. The message quotes the journal template, the batch and the line number so you can find the exact line. The date on its own is never the problem: what matters is the combination of that date and the window that is currently open. Finance teams keep that window narrow on purpose, so a blocked posting is usually the control working as intended rather than a defect.
Treat the allowed posting window as part of the month end routine: move Allow Posting From forward on General Ledger Setup on the day the previous period is signed off, and keep personal overrides in User Setup only for the few people who genuinely need to post into an older period. Checking the work date at the start of a session removes most wrong year mistakes, because new journal lines and documents inherit their posting date from it.
User Setup wins whenever it holds a value for the user who is posting. If that user has no User Setup record, or the two fields are blank there, Business Central falls back to the range on General Ledger Setup.
Only if you have permission to edit User Setup and General Ledger Setup, which is normally restricted to finance administrators. In most companies you have to ask them to reopen the period.