Common issues

Note: The character "$" represents a part of the error that could change, that is still the error you are looking for, and the specified fix should work for you

java.lang.UnsatisfiedLinkError: no $ in java.library.path (IntelliJ Idea)

Note: this error's "$" is often "lwjgl" or "lwjgl64"

If you are encountering this issue it means you haven't set the working directory to the MCP's jars folder.

Fix

1. Edit your run configuration
2. Change the working directory with "MCP_LOC\jars", where "MCP_LOC" is the location you have decompiled the MCP in

Unrecognized option: -Xincgc (Eclipse)

This is caused by a default argument that is not supported by the jre you are using. It could mean you're using Eclipse's jdk, which is 11 or higher. There are two ways to fix this issue The first one requires you to change the used jdk to 8. (Even if you only have Java 8 installed, it doesn't mean that that's what eclipse is going to default to. In fact, newer versions of Eclipse comes with jdk 11 bundled and used by default.)

Fix 2

1. Click on the arrow key next to the "Run" button
2. Click on "Run Configuration..."
3. Click on "Arguments"
4. Remove "-Xincgc " from the "VM Arguments", leaving no space before the next argument

Unable to add $ to system class path - the system class loader does not define the appendToClassPathForInstrumentation method or the method failed

This might be caused by a Non-ASCII character present in your Eclipse installation path.

Possible Fix:

Re-install Eclipse with a different path, that contains ASCII characters only.

NSException (MacOS)

When launching the client no window is actually created and then the client crashes with the following error.

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'NSWindow drag regions should only be invalidated on the Main Thread!'
*** First throw call stack:
(
	0   CoreFoundation                      0x00007fff34dcbb57 __exceptionPreprocess + 250
	1   libobjc.A.dylib                     0x00007fff6dc5c5bf objc_exception_throw + 48
	2   CoreFoundation                      0x00007fff34df434c -[NSException raise] + 9
	3   AppKit                              0x00007fff31fee5ec -[NSWindow(NSWindow_Theme) _postWindowNeedsToResetDragMarginsUnlessPostingDisabled] + 310
	4   AppKit                              0x00007fff32018cee -[NSThemeFrame setStyleMask:] + 137
	5   AppKit                              0x00007fff32018b3c __25-[NSWindow setStyleMask:]_block_invoke + 1908
	6   AppKit                              0x00007fff3201836e NSPerformVisuallyAtomicChange + 132
	7   AppKit                              0x00007fff32018279 -[NSWindow setStyleMask:] + 184
	8   liblwjgl.dylib                      0x000000011adacee2 Java_org_lwjgl_opengl_MacOSXDisplay_nSetResizable + 82
	9   ???                                 0x000000010860f6c7 0x0 + 4435539655
	10  ???                                 0x00000001085ff2bd 0x0 + 4435473085
)
libc++abi.dylib: terminating with uncaught exception of type NSException

Cause 1

The most common (if not only) cause for this problem is Java version higher than 8u251 (1.8.0_251)

Fix

The fix in this case would be to uninstall the current Java version and install Java JDK 1.8.0_251 (or lower) - make sure to update the jdk path inside of your IDE.