To find out why you are getting this error you should enable logging.
First, enable Failed Request Tracing for the web management service. You can see how to do this by referring to the "Optional: Set Up Tracing" section of this article:
http://learn.iis.net/page.aspx/984/configure-web-deploy/
The "frebs" can be found in:
C:\inetpub\logs\wmsvc\TracingLogFiles\W3SVC1
Open each of the frXXXXXX.xml files with IE and it'll use the freb.xsl transform to generate a nice report.
Don't delete freb.xsl when you're done, it doesn't always get recreated.
Then turn on logging for the web management service:
http://technet.microsoft.com/en-us/library/ff729437(WS.10).aspx
You want to have the following registry entry configured:
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\IIS Extensions\MSDeploy\1]
"EnabledTraceLevel"=dword:00000002
"EnabledTraceSources"=dword:000001ff
You can fiddle with the tracing levels/sources to increase and decrease the verbosity of the logs.
As per the article the management service logs are written to:
%WINDIR%\ServiceProfiles\LocalService\AppData\Local\Temp\WMSvc.log