Sorry I didn't copy/paste the actual code because I changed it to the working Textbox version I mentioned, so I introduced some red herrings on the board that are not part of the actual code.
First, the variable is not called var, that was just a dummy name, it's called window.unencryptedresponse.
Second, there are in fact quotes around the C2 data structure (either the ajax or textbox etc), here's the actual call.
Browser.ExecJS("window.unencryptedresponse=encrypt ('mykeystring', atob('" & AJAX.LastData & "'), 0, 0,0, 1); ")[/code:23l4u1k7]
encrypt is the enryption function and its various parameters, atob and btoa are functions that convert from base64 and back.
This is another call that fails for the same reason:
[code:23l4u1k7]Browser.ExecJS("window.encryptedresponse='" & AJAX.LastData & "';") [/code:23l4u1k7]
All of these actually work when using Textbox.Text instead of AJAX.LastData, (but not when using TextLabel.Text). So that makes me fairly convinced that it must be some illegal characters in there that Textbox does not support and removes, and that error message is known to come up in chrome in those zero-width-space situations.