Hello Sommer,
By default, all links you add to Marketo Emails will get additional parameters in order to track clicks to the link. Some websites do not support URL parameters and the links don't work.
For these sites you can disable the tracking code from being added to the link, take a look at the following article for instructions:
Disable Tracking for an Email LinkI hope this helps to point you in the right direction!
Reza.