These are the messages, but don't see any hint, for that issue:
Nachrichten, Hinweise: 154
Note: Duplicate unit "ZSybaseToken" in "zcore 7.1", orphaned ppu "C:\Development\lazarus_external_lib\ZeosLib\packages\lazarus\lib\x86_64-win64\ZSybaseToken.ppu"
...
Projekt kompilieren, Ziel: _bin\x86_64-win64\DbSrvForm.exe: Exit code 1, Fehler: 1, Hinweise: 2
Hint: Start of reading config file C:\Development\lazarus\fpc\3.0.0\bin\x86_64-win64\fpc.cfg
Hint: End of reading config file C:\Development\lazarus\fpc\3.0.0\bin\x86_64-win64\fpc.cfg
Verbose: Free Pascal Compiler version 3.0.0 [2016/02/14] for x86_64
Verbose: Target OS: Win64 for x64
Verbose: Compiling DbSrvForm.lpr
Fatal: Compilation aborted
Verbose: C:\Development\lazarus\fpc\3.0.0\bin\x86_64-win64\ppcx64.exe returned an error exitcode
I also tried to use my delphi mode generic code in a new project, but there it works fine. The only thing I recognized is, that in the project where the error occuers, the compiler doesn't complain when I use my generic class the delphi way without declaring that unit as {$mode delphi}.
e.g.:
var
x: TSimpleDict<Integer>; //compiles without {$mode delphi}
But adding that compiler mode, doesn't change anything.