From https://archive.sap.com/documents/docs/DOC-49467
Frequent issues on MD04
The most used transaction in PP-MRP is the stock/requirements list.
Issues from many different application areas are reflected in transaction MD04, since this transactio reads data from many different tables.
On this document you will find the most frequent issues observed on transaction MD04.
1 – An MRP element is displayed on transaction MD04, however, it does not affect the available quantity, that means, it is not MRP relevant.
This issue can happen for many different planning elements, from sales orders to dependent requirements and there are many different causes for this issue.
On the following note you will find a detailed explanation for the possible causes for each different planning element:
1825187 – MD04/MD05: Incorrect quantity for an MRP element
2 – Database inconsistencies
A planning element that is already completed is still displayed on MD04 or a planning element is incorrectly displayed on MD04. It generally happens for sales orders or for subcontracting requirements but it can also happen for another planning elements, such as dependent requirements. The following WIKI describes each inconsistency and how to correct it:
3 – Exception messages
There are usually several questions related to exception messages, for example, why an exception message appears on MD05 but not on MD04. The answer to this and another questions can be found on the following note:
550441 FAQ: Exception messages in material requirements planning
From all the exception messages, those related to the rescheduling check are the most frequent cause of issues. There is a lot of documentation about rescheduling and the following WIKIs and notes should be useful:
550302 FAQ: Rescheduling check
1745312 MRP creates redundant proposals though there are fixed future receipts which can cover the requirements.
http://wiki.scn.sap.com/wiki/display/ERPMan/What+is+rescheduling+and+how+does+it+work
4 – Why a planning element is displayed on MD04?
The following WIKI explains how to analyze MD04 in debug and find out where a planning element is comming from and why it is displayed on MD04:
http://wiki.scn.sap.com/wiki/display/ERPMan/How+to+analyze+the+MRP+elements+by+debugging
5 – Issues related to sales orders:
See the following document:
MD04: Problems with sales orders