I assume the share is actually "Build Archive," if so, then you would want to put incoming as the destination to copy to in the job.

I tried with and without incoming but both fail.
smb://domain;username@machine/Build%20Archive%2F
also fails.
It works only if I leave the Share Name blank and I put the share name in the destination path.

Why are you adding a trailing slash to the share name?

Trailing slash or not, it still doesn't work. The space in the Share Name is enough to make it fail.
Also, we are trying to get parametrized share name for a standard destination to all our projects, such as smb://domain;username@machine/Build Archive/incoming/$JOB_NAME/$BUILD_NUMBER
See HUDSON-8730

The share portion of the argument is the first part "Build Archive", the rest is a relative path to the root of that share, which should go in the destination field of the job configuration. I will try a share name with a space later.

Our reasoning is that we would enter the parametrized share name once and then select it from the drop down menu when configuring a project which is much less error prone.
I guess our request could also be to have standard destinations for a given share that would be configured in the global settings at the same time as the share. The share and the standard destinations would then be selected from drop down menus.

This is not currently how the plugin works. The share name entered on the global configuration page is THE share name, there should not be any additional path information. This is why slashes, et al, are getting escaped right now. Please open a separate request for the feature and I will debug the share name with space for this specific case.

Found that only the domain, username and password need to be URL encoded. So, I removed the URL encoding on the rest of the URL. Slashes in share names may still not work, but you filed a new issue on that request for default shares with variables.