[X4U] External Blu-Ray writer

[Paul Moortgat]

After I finished a movie in FCP X I would write it to a Blu-Ray disk.  It can't.  I get a message that's there's an error.  And I'm asked if the boot device has enough space.  There's 1.7 TB space.
Can it be that an external Blu-Ray writer is not the same as an internal one?  Then I send the movie from FCP X to Compressor 4 and tried to burn the file via Toast 11.  Then I got an error 5.  I've to ask Roxio what that might be.
The Pioneer writer is connected with a sata cable to a Sonnet card.
The only thing I can do is burn a DVD with the internal writer.
It's a Mac pro with OS 10.6.8 and 10 GB ram.  One MUST have OS 10.6 to run FCP X.
Any idea what to do?

Paul Moortgat