if you use the recent projects list to open a project, and that project no longer exists, the loaded project is closed before the new one fails to load. this leaves no project loaded in "st_project". the whole of standardTrackerGUI assumes that st_project is always a project. either... change that behaviour so that st_project can never become empty , e.g. by opening a new project when the chosen one fails to load --or-- change the assumption in standardTrackerGUI so that behaviour is appropriate when no project is loaded (i.e. the user is warned and told how to create a new project). the latter is probably more robust.
One drawback of Video Servers is that at the moment - if i remember right - there's no way to change jobs to use them after you've already created the jobs. That is, if an appropriate video server exists when the job is created, it is used, otherwise the job will always have a hard-coded path. I could add a facility to do this if it's important to you - in any case it's on the TODO list for the next version. NB to self: This is easy to do, from the job's perspective, you just have to call "job.setVideoFilename(job.getVideoFilename())" on the job. generally, are video servers implemented sensibly?
On a related note, "Find Missing Videos" does not work under certain circumstances. Try (a) Create a job, (b) Unload an delete the video, (c) Load up and use "Find Missing Videos" to reconnect. Next, try doing the same, but at (b) also delete the preview file. Something goes wrong, perhaps in both cases?