We've recently run into this, now occurring on all our Lenovo Laptops (T61, T400s, X300)... during the encryption process.
If Symantec Endpoint 11 (MR4) is installed, then we install Safeguard Easy or Enterprise, we get tonnes of "Windows Delayed Write Failed" error messages for seemingly random files. During encryption, there are random things going on on the computer, like some patches, few software installs, inventory. None of these things are extremely intensive. In fact, when I watch perfmon, things aren't crazy at all. Disk queue length is low.
As soon as I take SEP 11 out of the picture, no delayed write failed errors.
We need an answer on this too. It's not acceptible to leave the computer completely unprotected while safeguard encrypts the drive.
I've opened a support case with Sophos too, to see if they have anything they can pinpoint.