When I try I get this message:

Please supply us with a bit more of information so we can frame the source of the problem. 1) Could your current installation be corrupted and if so would you be able to uninstall completely Nexus and make a fresh install (our last resort)?; 2) Which Nexus are you using, the free version or Nexus Ultimate? When was the last time any of these had an update? Winstep homepage lists the last update of products in March 22, 2012. If you are using the free version you can simply download it again. For the Ultimate you may need the key. Install the free version and then register it with the key. [This worked for me in Xtreme. I downloaded the trial and then registered it. I had done a clean install of the system.] So it should work with Nexus too.

At this point it seems to me you should not have any updates if you installed Nexus after March 2012. But it would be great if we could understand the source of the error report. 1) Can be an internal error of the update manager, because there's nothing to update or the manager is corrupted (try to get it fresh in a new install, if it comes to that); 2) And then there's a whole host of other issues we would have to check if none of the above helps: does the manager have write permissions for the temporary folder? does it have those permissions to overwrite the setup file?

See if this suggests you something. And please, it is not required but I would appreciate if even with the problem solved you came back to this thread and tell us how that went.

this has been addressed before in the forums, please search them. since it's been over a year since the last winstep update no one should be on an older version.