It sounds to me like the connection between your DB server and CF server is
dropping. Where is the DB server in relation to the CF server? Did the DB
get taken down for maintenance? Is the problem always at the same time of
day? what time of day is that? Does it happen for ALL queries? When the
problem is manifesting, can you make a connection from the CF server to the
DB server using [insert name of appropriate DB client software here]. Can
you even ping it during these times? Does anything get logged on the DB
end of things?
There's plenty of invesigation here for you to do.