第一个：
[2012-11-09 13:15:14 - Tesa] Android Launch!
[2012-11-09 13:15:14 - Tesa] The connection to adb is down, and a severe error has occured.
[2012-11-09 13:15:14 - Tesa] You must restart adb and Eclipse.
[2012-11-09 13:15:14 - Tesa] Please ensure that adb is correctly located at ‘D:\学习\android-sdk-windows\platform-tools\adb.exe‘ and can be executed.
这个解决方法有多种：
1.进程中强制结束adb.exe，再重启Eclipse。
2.如果上面方法不行，看一下有没有类似91手机助手等工具正在开启，占用了该进程，有的话就关掉。
3.我遇到的问题的解决方法：把tools文件夹中的adb.exe复制到platform-tools文件夹中，是从网上看到的方法，我用的2.3AVD。
第二个：
[2012-11-09 13:35:03 - Emulator] WARNING: Data partition already in use. Changes will not persist!
[2012-11-09 13:35:03 - Emulator] WARNING: SD Card image already in use: C:\Users\LK\.android\avd\2.3.avd/sdcard.img
[2012-11-09 13:35:03 - Emulator] ko:Snapshot storage already in use: C:\Users\LK\.android\avd\2.3.avd/snapshots.img
查了好多方法，都没有太多效果。实际只需要把这两个文件（sdcard.img snapshots.img）删掉即可，删除之后会红色提示，随后打开虚拟机：
[2012-11-09 13:35:59 - Emulator] WARNING: Data partition already in use. Changes will not persist!
[2012-11-09 13:35:59 - Emulator] WARNING: Cache partition already in use. Changes will not persist!
2012.11.14
Field Requires API level 5(current min is 1)
project folder > Android tools > Clear Link Markers
2013.3.6
Unable to execute dex: java.nio.BufferOverflowException. Check the Eclipse log for stack trace. Conversion to Dalvik format failed: Unable to execute dex: java.nio.BufferOverflowException. Check the Eclipse log for stack trace
这种情况一般是直接Import工程时发生的。在工程中找到Android Dependencies,右键选择buid path,再remove it即可顺利编译通过。