In some places of sl-release-notes-6.3.html presented 6.2 release. For
example:
 
<H1>Scientific Linux 6.2</H1>

URLs on "Iso Download area"

Seems like sl-release-6.3-1.src.rpm, sl-release-notes-6.3-1.src.rpm,
hsqldb-1.8.0.10-9.el6.src.rpm missed in sl-source
repo.

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Best regards,
Elena