My last message was about this strange error I received. Today I got it again, which led me to believe a hardware failure was not the reason. So after some more investigation I found out Index Server was to blaim. Taken from (click here for full article):

If you run Index Server (Cisvc.exe), then Index Server may rescan the Temporary ASP.NET Files directory while it requests a Microsoft ASP.NET page. Cisvc.exe then holds a lock on the Temporary ASP.NET Files directory for one to five minutes. The length of time of the lock depends on the size of the directory that causes the Aspnet_wp.exeprocess (or W3wp.exe process for applications that run on Microsoft Internet Information Services [IIS] 6.0) to not load the particular DLL.