I got the error, after ho to center link of page in transitions modal window:
Please check the &url= parameter: it should to be a valid URL
How to reproduce:
ps: Without moving to another page in that transitions window, link opened is normal.
version of piwik: 2.0.3
In 32b677848db5bf4755b99a58375ff69b2f8d9e47: Fixes #4525 thanks for the report