Hi lalitha v
There is a fix here: https://github.com/jenkinsci/testlink-plugin/pull/35
There were some changes regarding how objects were persisted after a build. The Jenkins internal code also changed a little, in a way that the objects persisted are not always there.
The plug-in was basically trying to load sidepanel.jelly from the Run (an execution of the job, aka a build/etc). But since the Run was not persisted, it failed to load the sidepanel.jelly file.
The pull request fixes it, as it's possible to see in this screenshot.
The plug-in, however, needs more work before it's ready for a release. There are other parts of the code that are using deprecated API, the minimum version needs to be bumped up to the latest LTS release, more code can be removed (I threw away some code already in the PR), and, more importantly, I think we need to use the credentials plug-in for the XMLRPC API, to comply with the security best practices.
As I am not using Jenkins, and not using TestLink, I can't use my time from $work to work on this. And on my spare time I have a few other projects I'm either using or being sponsored that I need to fix first.
If you know some Java, and you can help with pull requests, I'd be happy to review/merge, until we get ready for a release. Otherwise, I will have long vacations in December, and *may* be able to cut a new release with a revamped version of the plug-in, compatible with the latest TestLink.
p.s. *may* because December is also summer where I live, and we have-so far-no lockdown over here, so I might be out of the city or spending time with family; but again, reviewing PR's takes only some minutes, or maybe one or two hours, which I can always squeeze in, and any Jenkins core/maintainer can release the plug-in, so that I don't bottleneck the process