0x00550008+0x00550008

Hi all: My sheduled backup fails when it tries to copy files to the Maxtor 1Tb external hard drive I get this event code 0x00550008+0x00550008 The knowledge base has no information about this error. I'm using Vista 64 bits and my Acronis build is 6053 Here's the error log:

<?xml version="1.0" encoding="UTF-8" ?>
<log build="6053" product="Acronis True Image Home"
   <event code="2" id="1" level="2" message="Operation My Application Settings Backup1 started." module="100" time="1266502176" />
    <event code="11" id="2" level="2" message="Priority changed to Low." module="100" time="1266502176" />
    <event code="24" id="3" level="4" message="Cannot proceed with operation while application is running.&#10;C:\Program Files (x86)\Mozilla Firefox\firefox.exe&#10;Close the application and click Retry. To stop the operation click Cancel.: None" module="85" time="1266502182" />
    <event code="8" id="4" level="4" message="Failed to copy file or folder ''.&#10; (0x550008)&#10; &#32; &#32;Tag = 0x3A4FB2E0331C3C5F&#10;Variable cannot be found. (0x550008)&#10; &#32; &#32;VarName = &quot;VISTA_VIRTUAL&quot;&#10; &#32; &#32;Tag = 0x945E498875687EBB: None" module="85" time="1266502192" />
    <event code="8" id="5" level="4" message="&#32;(0x550008)&#10; &#32; &#32;Tag = 0x3A4FB2E0331C3C5F&#10;Variable cannot be found. (0x550008)&#10; &#32; &#32;VarName = &quot;VISTA_VIRTUAL&quot;&#10; &#32; &#32;Tag = 0x945E498875687EBB" module="85" time="1266502201" />
    <event code="5" id="6" level="4" message="Operation has completed with errors." module="100" time="1266502202" />
</log>

Any ideas what's the problem? Thanks! xavier