The reason why you can't save an ACCDB to MDB is because the file contains features not available in the older version.
Neither lookup fields or long text (memo) fields are relevant to this situation.
Things that may cause problems include:
- new field types - attachment fields, MVFs & column history, calculated fields
- new datatypes e.g. large integer AKA bigint, date/time extended
- new control types e.g. navigation control, modern chart, 'new style' tab control(?)
- newer default sort order
In fact Access lists many of these in the error message shown if there are multiple issues
View attachment 121471
Even if you have none of the other issues, the sort order has often been the problem for me as its easy to overlook.
This error will be seen if its the only problem:
View attachment 121472
In Database Options | General, change the default sort order from e.g. General to General Legacy
View attachment 121473
The database should then convert to MDB successfully
EDIT: I've just written this up as a new web article for future reference:
ACCDB files can normally be converted to MDB – either 2000 or 2002/2003 file format. However, the process will fail if the ACCDB file contains features not available in the older version. This article outlines the main reasons why the conversion can fail.
www.isladogs.co.uk