[Xymon] wrong values in RRD

I am using xymon 4.3.10.

My xymon client sends 2 values to the xymon server,

disk_free = 10404175872 disk_free_limit = 1000000000

The values displayed on the dashboard are correct. But xymon server stores a negative value for disk_free and zero for disk_free_limit. How can I make xymon stores the proper value to RRD?

<ds>
    <name> diskfree </name>
    <type> DERIVE </type>
    <minimal_heartbeat> 600 </minimal_heartbeat>
    <min> NaN </min>
    <max> NaN </max>

    <!-- PDP Status -->
    <last_ds> 10404155392 </last_ds>
    <value> -6.7819016393e+04 </value>
    <unknown_sec> 0 </unknown_sec>
</ds>

<ds>
    <name> diskfreelimit </name>
    <type> DERIVE </type>
    <minimal_heartbeat> 600 </minimal_heartbeat>
    <min> NaN </min>
    <max> NaN </max>

    <!-- PDP Status -->
    <last_ds> 1000000000 </last_ds>
    <value> 0.0000000000e+00 </value>
    <unknown_sec> 0 </unknown_sec>
</ds>

Thanks P3