Cause: Sales order site code and ship site code is e.g. S088, But in site master for site S088 doc_prefix found as 87 so that document id generated from “87” even though Sales order is created for site code S088.
Remedies:
Users should ensure that the prefex in site mater is correctly saved. e.g in site master for site S088 doc_prefix should 88 for site code S088 for which the Sales order is created. For Site master goto System -> System setup->Masters->Site