This is a bug within Mura where the javaloader is being set in a server variable by the first mura site to run then can't be read by other sites on the same server due to coldfusion sandboxing. To fix this open the cfstatic.cfc file and change these lines from server to application variables, the lines below have been updated:

%MURAHOME%\requirements\org\cfstatic\CfStatic.cfc

Code:
313: if( not StructKeyExists(application, '_cfstaticJavaloaders') ){

320: application['_cfstaticJavaloaders'] = cfstaticJavaloaders;

323: _setYuiCompressor (CreateObject('component','org.cfstatic.util.YuiCompressor' ).init(application['_cfstaticJavaloaders'].yui ) );

324: _setLessCompiler (CreateObject('component','org.cfstatic.util.LessCompiler' ).init(application['_cfstaticJavaloaders'].less ) );
A bug report has been created with Mura about this.