In Microsoft Dynamics CRM 2013, you will receive "An error occurred" when clicking on a lookup field on a form.
In Microsoft Dynamics CRM 2011, you will be able to retrieve results on the lookup. On save, it will fail with "The lookup could not be resolved to a record in the system. You must select the record for the system to use before you can save."
This only occurs on Chrome version 38, which was released October 7, 2014. This includes any build lower than 38.0.2125.111. The version numbers can be found here: Chrome Releases
Chrome 38 version 38.0.2125.111 will resolve this issue. It is recommend to apply the latest updates for Google Chrome.