[VE][47] End of document in prolog error using locally installed W3C validator

Hi,
 
I'm trying to get the W3C validator running on my server so I can validate internal intranet sites without having to copy and paste the HTML source. I've got the validator itself running and can access the front page, however any attempt to validate anything gives the following error:

Error [47]: "end of document in prolog"
I installed the validator using apt-get install w3c-markup-validator on Ubuntu 10.04 Desktop. Most other instances of the error above seem to relate to the validator being unable to retrieve the source code, however I get this error whether I do a file upload, direct input or check using a URL. Also, if I do a check using a URL, the source code is loaded successfully and displayed underneath, but I still get the error above reported against line 1 col 0. (The URL itself doesn't matter - Google, Microsoft, Amazon etc all return the correct source code but still give the same error).
 
If I run the following command given by the validator manually:
/usr/bin/onsgmls -n -c /usr/share/w3c-markup-validator/catalog/sgml.soc -R -wvalid -wnon-sgml-char-ref -wno-duplicate
I get the following error message:
/usr/bin/onsgmls:14190260.2208:E: cannot find "/usr/share/w3c-markup-validator/catalog/sgml.soc"; tried
I can then type in or paste HTML and then see a set of results - various things like 'ATARGET IMPLIED' etc so I assume its able to validate the document?
 
Since every example of 'end of document in prolog' I can find mentioned online also has the symptom of missing HTML source I don't really know where to look next.
 
Thanks in advance
Ian


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