I was having problems mounting/reading my UDF 2.5 formatted discs on my standard installation of Windows 7 Ultimate 64-bit.
Found out a MS KB article of updated UDF.sys drivers:
However, the current hotfix system of MS sucks badly: request URL, get a time-limited DL link, zipped/encrypted file with password, etc.
So I found the updated drivers (6.1.7600.16435) from MS,but unencrypted, no password and checked with virustotal.com
I don't have the Panasonic Vista X64 UDF drivers installed, so I don't know how well these gel together. So, YMMV, caveat emptor, etc.