You mentioned this:
I wonder if it has to do with this plugin?
Currently there are no plugins allowed on WordPress.com. Are you talking about a self-hosted WordPress install on WordPress.org?
To clear up any confusion, WordPress.com and WordPress.org are two different entities. At WordPress.com, we provide hosting, support, and tons of features for blogs. Users also have the option to purchase a variety of upgrades to customize the look and feel of their blog. WordPress.org is a software for self-hosted sites. With WordPress.org, users are provided access to all backend files and can upload custom themes and plugins.
Check here to learn more about the difference between WordPress.com and WordPress.org:
If you are talking about a self-hosted, WordPress install, please contact your host for support.
If you are talking about WordPress.com and can you provide me the site that you are trying to access the Dashboard of?
You also mentioned this:
(c) Exactly what you experience including what any error reports you receive state.
Can you please elaborate on that?