The new XML parser in Tomcat 6.0.19 and Tomcat 6.0.20 is case-sensitive and may be related to this problem.
After you have applied Tomcat 6.0.20 patch, you find you can no longer deploy any WAR files. The context.xml file is created, but the WAR files are never expanded.
The problem appears to be related to the new XML parser in Tomcat 6.0.19 and 6.0.20 that is case sensitive. You need to check your context.xml file to make sure the "Context" tags are in upper case letter "C" and not lower case letter.