vim + ctrlp: coercing to Unicode: need string or buffer, long found

Question

I installed all plugins with vundle include ctrlp. Until I upgraded (:PluginUpdate) all my plugins, ctrlp was working fine.

However, now it displays coercing to Unicode: need string or buffer, long found for about 10 seconds before it disappears, only then I can use ctrlp.

How can I get rid of this error message?