Piston Cloud Computing, a San Francisco startup, found itself in this position in February when Red Hat Linux, the biggest commercial Linux firm, uninvited it from the Red Hat Summit which is scheduled to be held in San Francisco from April 14 to 17, according to CRN.

And the reason for the termination? CRN quoted an email from Michael Fremder, Red Hat's global corporate sponsorship marketing manager, which said effectively that it was done at Red Hat's "sole discretion".

Sponsorship doesn't come easy - Piston was paying out $US13,000 for the privilege, in days when the US economy is struggling.

Matthew Garrett, a former Red Hat employee who has gained something of a public profile, suggested that Piston had got itself into Red Hat's bad books by competing against it for a contract - and winning.

Noting that Red Hat had a culture which was highly conducive to open source, Garrett wrote that this occurrence should "trigger an examination of whether the reality of the company culture still matches the theory".

Asked why Piston was excluded, Red Hat's director of corporate communications Stephanie Wonderlick responded: "We made a mistake, and the original decision was not properly vetted within Red Hat.

"We apologised to Piston, and look forward to welcoming them to Red Hat Summit as our guest. Piston has confirmed that they will be there."