Problem: Clicking on New > Appointment or New > Meeting Request from the Standard toolbar in Outlook does nothing. Typing directly into the calendar and then navigating away produces the error, “Could not save item.”
Hmm: Googling this issue yielded the usual Outlook suggestions, but no explanation. The following is what worked for me. Your millage may vary.
Solution: From the menu bar, Tools > Options > Other > Advanced Options > Custom Forms > Manage Forms > Clear Cache.
Explanation: I didn’t dig into exactly how the forms cache is used. If you have a proper explanation, please enlighten us in the comments below.