Hi,
Is this the same value you had provided in the past for the dcPath param and it worked?
You didn't mention the version of vCenter you are working with but it's possible your embedded ampersand (%26) might be throwing a monkey wrench into the request handling so to speak.
I'm not familiar with how this is handled on the vCenter side of things but it is a possibility, especially if there are any rewrites/redirects being applied to the request. It wouldn't be the first time.