2.61 - Missing wysiwyg after upgrading from v2.01 / v2.14

I just installed a fresh version of CMB connected to a brand new database to see if I could fix what I've encountered but so far no luck. The data is there, and I can see it when using firebug and when disabling the visibility CSS, but the tiny_mce interface is not loading.

Here's the background:

1. Upgraded an old install on Site A (2.01) to a slightly more recent version (2.14) in order to match it with another functioning installation on the same server (Site B). 
2. After a 'successful' upgrade - wysiwygs are missing on Site A.  Essentially the same descriptions of missing wysiwygs archived on the forums.  The Site B has fully functional wysiwygs.
3. Copied the tiny_mce folder from the Site B to the broken Site A, figuring the folders should be identical now that they're both 2.14. Wysiwygs still missing on Site A, still working on Site B. 
4. Thought it might be time to purchase the upgrade to 2.61 (Build 1058) so I did, and installed it on Site A.  Still no wysiwigs.
5. Rolled back to 2.01. Still no wysiwigs.
6. Figured that might be because of something preexisting in Site A's setup, so I tried a fresh install in a new folder, with a brand new db.  Still no wysiwigs.

At this point I'm tired of the acronym 'wysiwyg' but it's pretty accurate - I'm not seeing anything and not getting anything lol :)

I have attempted everything I found on the forums with regards to possible cache issues, double compression issues, bad installations, bad "realpath" structures etc.  No Luck - though I may not have applied the double compression fix properly.... Both the fresh install of 2.61 and the old 2.01 throw the following errors in firebug (minus the actual location):

NetworkError: 500 Internal Server Error - http://www.mysite.com/cmsAdmin/3rdParty/tiny_mce/tiny_mce_gzip.php?js=1&plugins=inlinepopups,contextmenu,table,fullscreen,paste,media,spellchecker&themes=advanced&languages=en&diskcache=true&src=false

ReferenceError: tinyMCE is not defined
tinyMCE.init({

No 500 error is given if the URL parameters are removed from the above network error.

I was concerned that our server might not be updated enough to run 2.61 but it appears that we should have no problems.  Here are my server details for a sanity check:

• MySQL v5.5.35
• PHP v5.2.17

The content is still live for Site A - but my content managers have no way of updating wysiwyg content.  I'm getting ready to provide them with new editors, but I need to get this bug fixed first. At minimum I have to get the wysiwyg boxes working again in the 2.01 original install.  2.14 update would be great - and 2.61 even better.  Apologies if this isn't making sense - after trying to figure this out for several days I'm stumped and possibly incoherent :)  Thanks in advance!