Remove a spurious printf.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Lwt client was calling Ack twice.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Catch exceptions and return the exception as a string (for now)

We need to decide how to represent error messages.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>