>The SQL is :
>
>

SELECT prototype.*, trknum.*
>FROM trknum INNER JOIN prototype ON trknum.trknum = prototype.trknum;

>
>TRKNUM only has 1 field: TRKNUM and it is the primary key
>PROTOTYPE has a bunch of fields with ID being the primary key

I think that the update query cannot find the unique field to be updated due to the lack of a where clause. What trknum is going to be updated? The way the update statement is written all trknums would be changed to the value in mtxt0.
Also is prototype the name of the query or are you trying to refer to the base table?