Forms :: Cannot Open Any More Databases

I am using an Access 2007 front end linked to an Access 2007 back end. I have a Report that the user operates by selecting the information he/she wants to see on a pop-up form and clicking a button. The Report works perfectly unless another form, called Shows Form, in the database is opened. When Shows Form is open the Report/button on the pop up form generates Error 3048: Cannot Open Any More Databases. Also when Shows Form in open, the Query that the Report calls on also won't run. The Query gives gives the same error - Cannot Open Any More Databases.

I have been through my code with a fine tooth comb to make sure all DAO.Recordsets and DAO.Databases are closed after they are used. The troublemaker Shows Form is quite complex and has many sub-forms (11), on a tab control (9 tabs). The Shows Form is the work horse of the database and the User needs to have this form open all of the time. It is inconvenient to have to close the Shows Form in order to use the Report. I am suspecting, through my internet reading, that the multiple sub-forms in the Show Form are using up resources and causing Error 3048.

I thought maybe I could look at coding the sub-forms to open only when needed - when the user clicks on the tab containing the sub-form. Would that conserve resources?