We've experienced some annoying bugs with workflows since the RTM version of MOSS. After spending a lot of time trying to fix them or make workarounds, Lucy, our workflow girl, has been busy solving them. With success! After her first post about a delay activity (which can be downloaded here), she solved one of the bugs we've been facing for a long time now.
"A few months ago I was experiencing a rather annoying bug, a ‘Server Error in '/' Application’ when using my custom workflow on a publishing pages document library in MOSS 2007. The issue was: If my custom workflow is applied to a publishingpage, when the user enters the document library and selects ‘Edit Properties’ or opens the page for editing the server error pasted below occured. When check out is disabled on the document library the error does not occur when editing properties, However the user still cannot edit the page through ‘Edit Page’. The user can check in and check out the page without any problems."
"After discussing the issue with Microsoft and placing a call, yesterday the final answer came through in the form of a hotfix, related to KB Article Number 933819. The knowledgebase Article seems to be taken offline but yes! It is the answer. I applied the hotfix to my server and instantly the error has disappeared. My workflow is working beautifully now.
So, if you are experiencing the same bug, give Microsoft Support a call and mention KB 933819."
Check out the whole article here