I get this with Chrome against a Solaris server:
Uncaught TypeError: Cannot call method 'setDesktopSize' of undefined ui.js:55
(anonymous function) ui.js:24
Probably because we try to call setDesktopSize before we've set up the RFB object.
There might be more races in the code as I'm often getting problems against the Solaris server where everything just stops whilst loading the page.
The code has been improved (and the issue described in the description of this bug was fixed) in the rewrite done by upstream which was brought to ThinLinc in commit r29596.
Code review has been done and additional fixes to improve rubustness were commited upstream in 3b8ec46.
Fixed by vendordrop in r30096 and in commits r30097 and r30098.
Added some long delays to the web server, but I could not provoke any errors.
One of the changes brought in by the vendordrop in r30096 causes backspace and non-US characters to stop working when using the on-screen keyboard on Android devices.
The issue was a silly typo which is fixed in r30324.