You are using tracked links in your emails and the mkt_tok tracking token URL parameter is too long for some of your systems.
There is not a way to make the mkt_tok tracking tokens shorter. These tracking tokens must be this length in order to attain uniqueness for each individual Marketo record across all databases of all Marketo Clients.
It is possible to remove the token while keeping the link tracking. You can do it from the Edit Link window in the email editor.
Or you can add a "class="mkt_NoTok" to your HTML to disable it for larger blocks of content.