Ok, I may not be following all this, but ...
1.9.+ themes are not compat with 2.x anything.
Does theme directory have a 'wavelength' directory in it? Is it a 2.x theme?
If you think it's the 'wavelength' 'WaveLength' issue (Unix/Linux are case sensitive) then 'go with the flow' (until one figures out the issue):
in the moodle code theme folder
(example: /var/www/html/moodle23/theme/)
cp -rp wavelength WaveLength
That copies all the files/subfolders in wavelength to a folder called 'WaveLength' and preserves ownership/permissions. Any client calling for that or anything in your Moodle calling that will find it.
If your theme is such that you can't even login to Moodle, use the config.php file and insert the following:
$CFG-> theme='boxie';
or one of the standard themes that come with version 2 of Moodle.
The ';' is important at the end of that line.
Once you get logged on and have changed the default theme, don't forget to flush the theme caches. Check it out from another machine/flavor of browser.
Finally, when/if the theme issue is resolved, comment out the line added by putting // in front of it. No need to restart server/service. It's there then in case more themeing snafu's arise and easy to get back into Moodle then.
'spirit of sharing', Ken