Possible reasons leading towards the error:

1.The error may occur if you have the artifact with .lastupdated , because of network issue sometimes the plugin doesn’t get installed correctly.

2.Also there is a chance to get Missing artifact exception if you don't have Apache Maven installed.

Possible Solution:

1.Check if the jar file is present in user_home/.m2 repository? I have attached screenshot of path for reference. It will be under .m2\repository\com\tibco\plugins\com.tibco.bw.palette.shared\6.1.100 directory.
If the file name has .lastUpdated appended, remove it, renamed the jar and pom files. Once done, executed the goal again.

2.Check if com.tibco.bw.palette.shared artifact is not present in .m2 repository. So if it is not present in .m2 repository that means maven plugin is not installed properly and you will need to install it again.

Error-Missing-artifact-com-tibco-plugins-com-tibco-bw-palette-shared-jar-6-1-100-after-generating-for-application

github