After creating a new draft newsletter, I click "Save" to save it. I get "There has been an error." If I enable dev mode, this translates to the following error. How can I fix it? It hasn't happened previously -- it's just started happening all of the sudden:
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ERROR:Error 256: Unknown Email ID: 40
At l443 in [...]code/NewsletterAdmin.php
user_error(Unknown Email ID: 40,256)
line 443 of NewsletterAdmin.php
NewsletterAdmin->getNewsletterEditForm(40)
line 230 of NewsletterAdmin.php
NewsletterAdmin->NewsletterEditForm()
line 214 of NewsletterAdmin.php
NewsletterAdmin->EditForm()
line 169 of Controller.php
Controller->run(Array)
line 104 of Director.php
Director::direct(admin/newsletter)
line 158 of main.php