Updates problem with NIS 2010

Hello,

everything has been going great with NIS 2010 so i havent had to post for a long while, but since the 13th Feb i have had a problem with the updates, when i run update it checks and downloads and then tries to install and tells me something like " Process Updates - Failed to install all updates" and i have to run it a second time, on which it downloads a 1.1 mb update and tells me its ok.  after that its alright, but why is it happening  and is there a fix to stop the error occuring?

Thank you.