OK, here is a recipe to see this problem.  I hope all the
steps are here!

(0) Install drbd8-utils and heartbeat.
(1) Create a fake disk
dd if=/dev/zero of=drbd_disk count=1M bs=1
losetup /dev/loop0 ./drbd_disk
(2) Create /etc/drbd.conf.  I used:

global {
  usage-count yes;
}
common {
  protocol C;
}
resource r0 {
  device	/dev/drbd0;
  meta-disk internal;

  on maisy {
    disk	/dev/loop0;
    address	192.168.0.4:7788;
  }
  on hazy {
    disk	/dev/loop0;
    address	192.168.0.5:7788;
  }
}

(3) Create the drbd disk:
drbdadm create-md r0
modprobe drbd
drbdadm attach r0
drbdadm syncer r0
drbdadm connect r0
mkfs.ext3 /dev/drbd0

(4) Turned off drbd: /etc/init.d/drbd stop 
Stopped the drbd init script from running at startup (to avoid clashes
with heartbeat):
update-rc.d -f drbd remove

(5) Created /etc/ha.d/ha.cf, contents:

autojoin none
mcast eth2 239.0.0.43 694 1 0
warntime 5
deadtime 15
initdead 60
keepalive 2
node maisy
node hazy
crm yes

(6) Created an appropriate /etc/ha.d/authkeys file.

(7) Set up resources and constraints:

cibadmin -o resources -C -x resources.xml
cibadmin -o constraints -C -x constraints.xml

where these files contain:
resources.xml:

<resources>
  <master_slave id="ms_drbd_files">
    <meta_attributes id="ms_drbd_files-meta_attributes">
      <attributes>
        <nvpair name="notify" value="yes" id="ms_drbd_files-meta_attributes-notify"/>
        <nvpair name="globally_unique" value="false" id="ms_drbd_files-meta_attributes-globally_unique"/>
      </attributes>
    </meta_attributes>
    <primitive id="drbd_files" class="ocf" provider="heartbeat" type="drbd">
      <instance_attributes id="ms_drbd_files-instance_attributes">
        <attributes>
          <nvpair name="drbd_resource" value="r0" id="ms_drbd_files-instance_attributes-drbd_resource"/>
        </attributes>
      </instance_attributes>
      <operations>
        <op id="ms_drbd_files-monitor-master" name="monitor" interval="29s" timeout="10s" role="Master"/>
        <op id="ms_drbd_files-monitor-slave" name="monitor" interval="30s" timeout="10s" role="Slave"/>
      </operations>
    </primitive>
  </master_slave>
  <group id="rg_files">
    <primitive class="ocf" type="Filesystem" provider="heartbeat" id="mount_data">
      <instance_attributes id="mount_data-instance_attributes">
        <attributes>
          <nvpair name="device" value="/dev/drbd0" id="mount_data-device"/>
          <nvpair name="directory" value="/mnt" id="mount_data-directory"/>
          <nvpair name="fstype" value="ext3" id="mount_data-fstype"/>
        </attributes>
      </instance_attributes>
    </primitive>
  </group>
</resources>

constraints.xml:

<constraints>
  <rsc_order id="files_after_drbd" from="rg_files" action="start" to="ms_drbd_files" to_action="promote" type="after"/>
  <rsc_colocation id="files_on_drbd" to="ms_drbd_files" to_role="master" from="rg_files" score="infinity"/>
</constraints>

(8) Started heartbeat: /etc/init.d/heartbeat start

(9) Observed the following failure in the system logs:

May  4 15:09:11 maisy lrmd: [4150]: info: RA output: (drbd_files:0:start:stdout)  
May  4 15:09:11 maisy drbd[4491]: [4549]: DEBUG: r0 start: Module loaded.
May  4 15:09:11 maisy drbd[4491]: [4551]: DEBUG: r0: Calling drbdadm -c /etc/drbd.conf state r0
May  4 15:09:11 maisy lrmd: [4150]: info: RA output: (drbd_files:0:start:stderr) local: 586: state': bad variable name 
May  4 15:09:11 maisy drbd[4491]: [4558]: ERROR: r0: Called drbdadm -c /etc/drbd.conf state r0
May  4 15:09:11 maisy drbd[4491]: [4559]: ERROR: r0: Exit code 2

(10) Modified /usr/lib/ocf/resource.d/heartbeat/drbd to use "role" rather than "state".

(11) Restarted heartbeat: /etc/init.d/heartbeat restart

(12) Observed that there is no longer such an error in the system logs:

May  4 15:28:06 maisy drbd[6359]: [6370]: DEBUG: r0: Calling drbdadm -c /etc/drbd.conf role r0
May  4 15:28:06 maisy drbd[6359]: [6377]: DEBUG: r0: Exit code 0
May  4 15:28:06 maisy drbd[6359]: [6378]: DEBUG: r0: Command output: Secondary/Unknown