Which version of Windows are you using? Is this a work computer which is managed by your company's IT department?
When I Google that error number, some of the pages say that this error can happen if your IT department configured your computer to use a Windows Service Update Server (WSUS) and .Net Framework 3.5 was not approved by that server. You should probably contact your IT department for help installing .Net Framework 3.5.
Here is a page that talks about a workaround involving modifying the registry: