I have a WSP that contains a web part. It's being built using WSPBuilder. Most of the time, the WSP deploys perfectly. However, in two of our test environments (and sadly, in production, too) the WSP doesn't deploy properly to all the web front ends.

The assemblies make it into the GAC, and the .webpart files get provisioned. The problem is that a tool part that the web part relies on for configuration simply fails to appear. I've determined that every time this has happened, it has been isolated to a single web front end.

I've been able to resolve the issue by doing an stsadm -o deploysolution to re-deploy the solution, and in one instance it was resolved by the end user deactivating/reactivating the feature. Unfortunately, though, this has made it impossible to determine if the control isn't being deployed properly, or if it's some other issue.

Any thoughts on this? Could it be a problem with the WSP, or is it likely to be environmental?