Are all the PS2 thick backwards compatible or was it just the early models? I had a first gen (bought when the concele was first released) PS2, but it finally died after all these long years. So I got me a new to me one, when I went to play some of my old PS1 games, it said disk error.
PS2 of any version is compatible with all PS1 games (there are rare exceptions). Most probably it's just a technical problem with either disk and/or console itself. The PS2 is also known for it's disk error problem, quote:
A class action lawsuit was filed against Sony Computer Entertainment America Inc. on July 16, 2002, in the Superior Court of California, County of San Mateo. The lawsuit addresses consumer reports of inappropriate "no disc error" (disc read error) messages and other problems associated with playing DVDs and CDs on the PlayStation 2.
Sony settled its "disc read error" lawsuit by compensating the affected gamers with USD $25, a free game from a specified list, and the reduced cost repair or replacement (at SCEA's discretion) of the damaged system. This settlement was subject to the courts' approval, and hearings began in the US and Canada on April 28, 2006, and May 11, 2006, respectively.
But I'm not sure that "slim" models are affected with mentioned above problems.