>One of my screens allows the user to create temporary indexes on a table "on the fly." Since these are temporary, I create IDX files. However, I am running into a problem using transactions while these indexes are open. What I don't understand is why I should get the error in another form when each form is using a private datasession. Why should an open index in one form affect a transaction in another on a different table?

I don't know why, but apparently it does. The Visual Extend platform, for example, has a corresponding method to get rid of temporary indices in all open forms, precisely for this reason. Visual Extend uses temporary indices all the time, for user-defined orders (when the user double-clicks on a grid column, and an index with the correct expression doesn't exist, the temp index is created).