So I've been having a weird issue, and I was wondering if anyone else was experiencing it as well.
On the FTB launcher, I've been unable to launch anything except Ag Skies (1.6.4MC). Most of the options that won't launch are 1.7.10 and there are a few threads and vids around and about the 'net about 1.7.10 modpack launching issues, but I haven't been able to get the solutions suggestions to work.
Anyone else seeing this? Any suggestions?
What version of Java are you using?
EDIT: Sorry, what am I saying :P As in the launcher doesn't even attempt to launch the mod packs or it crashes when minecraft has opened and is loading?
Well, I'm using 8v66 64bit. But I think 7's been retired completely.
I'll click launch, and the launcher will respond -- seemingly, anyway -- graying out the buttons and so forth, but a minute or two later it just returns to it's default state without launching MC.
Under the advance options in the launcher, check it has the correct path to the Java JRE.
I don't see anyplace I could put a path string.
OK, so there is a "Java Path" heading, but it is by a drop down, not something I can put the JRE's path string into.
Ah okay. (they've changed it since I last played with FTB) But that was usually the root cause of most issues.
Enable the "Extra Launcher Debugging" and try launching again. See what it spits out. (if you need dump the error log in pastebin or something)
Ok, here you go. I feel really quite lazy now -- this was the only error I saw, at the very end of the log.
ERROR StatusLogger Unable to locate a logging implementation, using SimpleLogger
ERROR LaunchWrapper Unable to launch java.lang.ClassNotFoundException: cpw.mods.fml.common.launcher.FMLTweaker
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:106)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:98)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
[04:07:45] [DEBUG] Benchmark.logBenchAs:73: UnreadNews Init took 10 ms.
[04:08:29] Logs copied to clipboard
This suggests to me that maybe you were right in the first place, and FTB can't find javaw.exe?
The only point with which this doesn't make sense is that if it couldn't find Java. Why would one mod pack work and another doesn't.
What it might be related to is if you have that specific version of Minecraft downloaded via the default launcher. Try running 1.7.10 through the default launcher and then retry the mod packs that use that Minecraft version.
Doesn't change the error output, oddly.
So how do I fix the mismatch?
Its a bit odd to call what the issue is, simply due to the vague-ness of the error itself. But it maybe in relation to a bugged download (possibly?).
Under options click "Force Update" and try launching a modpack.
Failing that the only thing I can suggest without looking into other stuff is to delete the entire directory where the FTB launcher is installed and redownload the launcher.