When installing mods duplicate block and item ids frequently cause errors. I wrote a simple Perl program to find all the config files and report duplicates. It says how many it found in each config file and if any are duplicates and then prints a report of all ids found.
Once you get to paste bin, copy my entire post into Wordpad. Don't use Notepad, it's messes with what is typed and will mess up the program source code. In Wordpad save the new file as minecraft_find_ids.pl. ".pl" is the extension for the Perl computer language. Don't save it with the ".txt" extension.
But you can't run my program or script without installing Perl. But you can download it for free. Just search for "ActivePerl Download". The first one that comes in Bing will do. For Windows you want the Windows Installer (Msi). Strawberry Perl is another Perl for Windows. A Linux Perl would be ok too.
If you install Perl in the default place, your path to the Perl executable should be
which you will notice is the first line of my Perl script that you saved in Wordpad.
That first line is how a Perl script knows where to find the Perl executable.
If you change the Perl location, you have to edit that line.
Don't forget to keep the #! before the path.
Since the minecraft_find_ids.pl was saved with the ".pl" extension, its Icon should now be funny line with four stars around it.
Now put minecraft_find_ids.pl in you %APPDATA% folder and double click on its icon to run it. It just needs to be in the same folder as your .minecraft folder.
It will search your entire .minecraft folder for config files. It will find any types that I know about. So I might need to add more file types. It reports how many ids it found per file. So if you think a config file has some ids and the program didn't find them, then I need to enhance the program. It stores all the IDs and will report any duplicates as an error. So you will need to edit the config file by hand and fix the error. The program doesn't edit the files for you. After it scans all the files it generates a table showing all the ids it found and which file they where found in. It creates the report file "minecraft_id.rpt".
The mods create the config files so you need to try and run Minecraft, even if it crashes. Hopefully the config file is created before the crash. You can also run the mod as the only mod in your mod folder just to get it to run. Which will create the config file.
I noticed that some mods didn't work when I changed their IDs. I just changed that other config file that conflicted.
Oh, it dosn't matter how you run Minecraft. All ways seem to generate a .minecraft folder in the %APPDATA% folder that are all structured the same. This program runs outside Minecraft and just looks at the config files that mods creates.