I'm sorry to post this as I'm sure it will be corrected quickly in the current 5.0.x SVN. The solution could not build because of a faulty reference to ODFileUtils.CombinePaths in FormCommunications.cs which tried to combine 3 strings though it can only combine two. This error broke my previous testing build.
I simply converted the triple combine in butStationary_Click to two double combines as follows:
No prob. I'm now looking at CodeBase.ODFileUtils in the current /head, and see that a second 3 argument definition for CombinePaths is there which would fix the problem. I need to redownload OD5.0 source as it should also be there now.