[JavaScript] Quick Reply (Quote) Not Working

[sparkks]

This user has been denied support.

On my forum, I am able to press the "Quote" button, and the message below the Quick Reply Form will show:

You have selected one or more posts to quote. Quote these posts now or deselect them.

Once I press "Quote these posts now" I receive this error:

SyntaxError: JSON.parse: unexpected character at line 1 column 2 of the JSON data --- jquery.js:4:15940

Any one know a quick fix for this?
I know my posts have the proper ID tag around them.
I know it's not a template issue because it's not working with the default theme. 
I don't remember installing any plugins that could have caused this issue, via JavaScript.

Does anyone know where I can find this json table to fix the issue?

[jyotirmoy99]

replace "jquery.js" with fresh mybb pakage

[sparkks]

This user has been denied support.

replace "jquery.js" with fresh mybb pakage

OK.

I did this now we got a little further. Now the 'loading.gif' shows, but nothing happens.

[vovas]

Same error:

SyntaxError: JSON.parse: unexpected end of data at line 1 column 1 of the JSON data  jquery.js:5:15991
	m.parseJSON http://myforum/jscripts/jquery.js:5:15991
	Thread.multiQuotedLoaded http://myforum/jscripts/thread.js:116:14
	Thread.loadMultiQuoted/<.complete http://myforum/jscripts/thread.js:99:6
	m.Callbacks/j http://myforum/jscripts/jquery.js:2:27304
	m.Callbacks/k.fireWith http://myforum/jscripts/jquery.js:2:28122
	x http://myforum/jscripts/jquery.js:5:22237
	.send/b http://myforum/jscripts/jquery.js:5:26030

jquery.js from 1.8.10 package.