The file 'microsoft.reportviewer.winforms version 126.96.36.199 culture neutral publickeytoken..cannot be opened. Do you want to remove the reference to it from the Recent list?
Recently I did a SQL Server install and everything went fine. But then I tried to run a disk usage report on one the databases and got the above mentioned error
According to a ticket with Microsoft and this is a known issue.
You can verify this by checking if you have the following folder.
"C:\Program Files (x86)\Microsoft Visual Studio 9.0\ReportViewer"
There are two workarounds for this issue.
1) Download and install the Reporting Services Report Viewer 9.0. You can download this package from the Microsoft Download Center or by using the following link:
2) Additionally you can install "Business Intelligence Development Studio" using the same installation media that you used to install SQL Server. You can also download this from Microsoft's website. I guess you didn't install this while installing SQL Server.