I just started having the similar problems, not only on the Fidelity site but on others as well.
This is a brand new Dell Precision T7600 Workstation with Windows 7 SP1 x64 16MB of memory, Sata hard drives, etc (this is one of the most stable computers ever manufactured, meeting, complying and exceeding ISV-Certified standards) ...
I manage over 200 PC's with similar configurations. I've never seen this particular problem before. Nevertheless, since I've been researching it, apparently it has been going on for quite a while. It is happening to my customer using Adobe Reader XI (11.0.2). He only uses on his computer Microsoft Office 2010, AutoCad 2012 and Norton Internet Security. They have 19 other identical computers with identical hardware and software configurations. Only one up till now is presenting the problem.
The message is as stated above:
"There is a problem with Adobe Acrobat Reader. If it is running, please exit and try again. (523:523)"
Initially I thought it was an IE10 issue (since it started around the time IE10 was released and installed) but as I've investigated on the web over the last couple of weeks, it appears to also be happening on other versions of IE and FireFox, other versions of Windows as well as with other versions of Adobe Reader and Acrobat. The problem seems to be without a doubt an Adobe issue.
What is throwing me off is that I have 18 other computers of the same model, same updateswith identical software images as the one above. I've tried uninstalling and re-installing Adobe Reader, uninstalling again using Revo Uninstaller, using protected mode "on-off" solutions suggested on some forums, downgrading back to IE9, disabling all non-Microsoft startup items and many many other suggested fixes (even went to the extreme of removing Norton Internet Security completely just to be thorough). None have worked. My guess is that I will have to eventually wipe out the computer and do a clean install and hope the error does not reappear.
Also, the problem seems to be intermitent. At times it gives the error and once I click on "Ok" it opens the pdf document as if nothing had happened. At other times, closing IE10 and re-opening it solves the problem. Other times re-booting the computer solves it temporarily and other times, just going to another site with pdf files and opening them there and later returning to the website with the problem document allows us to open it without problems.
This behavior is very erratic, extremely disruptive and annoying to say the least. This seems definitely to be a bug with Adobe. I'm hoping that Adobe will "listen" and come up with a solution although my experience with Adobe over the years is that they do not even acknowledge issues (I know for a fact, by personal experience of errors and problems that have been annoying customers for years, error that are so persistent that they continue to annoy them trickling down from version to version and seen Adobe just ignore them.
My only advice, to whoever reads this, is to attempt some of the solutions described on a Google search or in this forum (some suggestions have worked for some users). Otherwise, make your voice be heard and post your complaint everywhere you can. It may be the only way to get Adobe's attention.