Strange error when inserting new sales order

We've been running Navision for over three years now, and all of a sudden today, when we tried to insert a new sales order we got this error.

You do not have read permission for the Sales Header Archive table

Which is correct, we don't have that granual (5160 i think).

I ran the debugger and this is the code from Sales Header OnInsert that was triggering the error (the IF FIND('+') line in the called codeunit actually caused it to "break on error")

"Doc. No. Occurrence" := ArchiveManagement.GetNextOccurrenceNo(DATABASE::"Sales Header","Document Type","No.");

This, afaik, is standard navision code, and I haven't modified it, or the codeunit it calls.

For the time being, since we don't the archiving granual anyway, i commented it out and put "Doc. No. Occurrence" := 1; so we could create sales orders again.

Anybody have any idea what would have triggered this problem? I'm at a loss.

If it makes any difference we're running 3.10 on a MSSQL server. We also have a development database that is identical to our production db, other than the data is old, and it doesn't give the error. Weird.