SQL Server 2008 R2 SQL Server has encountered x occurrence(s) of I/O requests taking longer than 15 seconds to complete on file '
Just a hunch... is that ldf growing when you get this error? I seen this error a few times and always been that someone set the growthrate in too big steps for the io subsystem to handle at same time as normal io within 15 seconds. Go and see if it happens to bet set to 10% and how big a step that would be. If it is GBs you might want to set it to a smaller size to grow and also in MB instead of percent.

Who knows I might get lucky on this one ;-)