I have a Contacts form which has a Calls sub-form which itself has a Subjects sub-form. From the Contacts form the user can click a button which writes a pro-forma letter from a selection. The application then updates the Call & allows the user to select the Subject(s) from the Subjects available (drop-down menu). If the user wants to write a second letter immediately, I get the above message. If they do anything else first, they are OK.
I have tried refreshing the Contacts form & each of the others at various points in the process, explictly saving the record (caused another error) etc. without success.
Can you help?

the error refers to a save and a requery which you haven't said anything about. do you know where the save and requery are occuring?

The main Contacts form has other sub-forms so there is a lot going one. It is difficult to describe. I've attached a picture.
The relevant forms are linked using Parent & Child fields:
Calls to Contacts using ContactID (bottom right)
Subjects to Calls using ContactID & CallID (left within the above)
The only thing that has changed (the forms have been in use for years) is that 2 fields on the Calls record have been replaced by the Subjects table. Hence the new sub-form. The only new QUERY I can find is the one which provides the drop-down menu for the Subjects themselves. The other fileds on a Subjects record are completed by the application. When the user selects a entry the application opens a new line in the Subjects form. This seems to be where the problem is. I have just found that another situation associated with this action which causes the same problem.
Hope this helps

Subjects to Calls using ContactID & CallIDshouldn't that just be CallID?

The other fileds on a Subjects record are completed by the application.it's hard to tell but i would check that this part is working properly, that the ID field is being updated and with the right data for ex.

When the user selects a entry the application opens a new line in the Subjects form. This seems to be where the problem is. I have just found that another situation associated with this action which causes the same problem.you said that if the user does anything else there's no problem. maybe you can make the app do something else - set the focus somewhere to mimic "doing something else". not much of a fix, i know. still a bit hard to tell what to do. btw, no pic attached.