Happened on a MacMini (OSX 10.4.11, ATI9200, PPC) some time ago:
Downloaded i guess the latest version, decompressed it, doubleclicked it, got an error message which told me that i have to reinstall BlitzMax, out of curiosity but without beeing convinced that this would be the solution i did that, so the whole thing from downloading the appropriate files (by the way the package under the 1.26 ppc version is broken), reinstalled, rebuild docs, updated the base installation, updated bmk, rebuild the files, retried and got the same error message as before that i need to reinstall BlitzMax...
Downloaded i guess the latest version, decompressed it, doubleclicked it, got an error message which told me that i have to reinstall BlitzMax, out of curiosity but without beeing convinced that this would be the solution i did that, so the whole thing from downloading the appropriate files (by the way the package under the 1.26 ppc version is broken), reinstalled, rebuild docs, updated the base installation, updated bmk, rebuild the files, retried and got the same error message as before that i need to reinstall BlitzMax...