Try taking the AAAA battery out of the pen and re-installing it. If that doesn't work, replace that battery. I had the same issues, and either re-installing or replacing always solves them. That size of battery can sometimes hang on the shelves for years, so it's possible for a brand new one to be DOA or die very soon after installation, so even if the battery is brand new you might still have problems.
Even if a new batch shows as good on my battery tester, they seldom last more than a few weeks anyway. -DA1