The memory used by the Windows kernel is either Paged or Non-Paged. Non-Paged means pinning the memory in physical RAM. Paged means it might be swapped out to disk and paged back in when needed. OP was working on BitLocker a file system driver, which handles disk IO. It must be pinned in physical RAM to be available all the times; otherwise, if it's paged out, an IO request coming would find the driver code missing in memory and try to page in the driver code, which triggers another IO request, creating an infinite loop. The Windows kernel usually would crash at that point to prevent a runway system and stops at the point of failure to let you fix the problem.