OK, I see what the problem is: the game record provides the FEN tag before the Variant tag. So when the game is loaded while WinBoard is not yet in FRC mode, the Variant tag will trigger a variant switch to FRC, which will also trigger a new shuffling of the start position. This has only a 1-in-96 chance of reproducing the position from the FEN tag, and in all other cases the following moves will no longer fit the start position. If I change the order of these tags, the game loads without problems. If WinBoard is set to FRC first, through the New Variant dialog, the game also loads without problems, irrespective of the tag order. This should be considered a work-around for the mentioned problem. I guess loading a game of a variant that is not currently selected is bound to cause trouble if the Variant tag does not come before other variant-specific tags, such as the FEN tag. Because the FEN would be parsed in the wrong context: piece IDs in the FEN can have different meaning in different variants, and even the board size could be different, or extra fields could be present (e.g. for recording the number of remaining checks in 3-checks) which would get ignored. Now the Variant tag is an extension to the PGN standard, and there is thus no official standard that explicitly declares the ordering of the tags as used by TCEC as illegal. Although a lot of misery could be avoided by declaring it is. Nevertheless, for the convenience of being able to automatically load such 'illogically encoded' games (e.g. when using the file association for loading the game by double-clicking the PGN file icon), it would be better to defer processing of a FEN tag until move number 1 is encountered. Op di., mrt. 1, 2022 om 20:47, Tim Mann schreef: I'm not really working on xboard or WinBoard anymore. I'm cc'ing the developers mailing list on this reply in case anyone else can help. On Tue, Mar 1, 2022 at 10:46 AM Vadim Trofimov wrote: Hello, Tim Mann, I really like your WinBoard program. I use Winboard 4.2.7 and Winboard 4.8.0 to watch games by downloading and opening the archive in pgn format. On the website https://tcec-chess.com/#x=archive (https://tcec-chess.com/#x=archive) there is an archive of computer engine games, for example, Season 21, where FRC 4 is Fischer Chess 960: Winboard 4.2.7 Winboard 4.8.0 does not show Fischer chess 960 games, they write an error message "Illegal move" on moves 0-0; 0-0-0 and other moves if there are comments in parentheses in the pgn text. In previous seasons, computer engines also played Fischer's 960 chess, and Winboard also writes an error message "Illegal move" on moves 0-0; 0-0-0. Please fix these Winboard errors to be able to view Fischer's 960 chess games.
PS: Archive of people's games in png format from the site chess-poster.com (http://chess-poster.com) WinBoard shows without errors. Best wishes, Vadim Trofimov from Russia
