In Didger 2 and 3, the Tools | Resample Polylines command is not available with raster projects. It is only available in vector projects. If you have a raster project, export the polyline(s) to a vector file format (like DXF or GSB), then import the vector file back into Didger into a vector project and perform the resampling.
Didger 4 and Didger 5 solve this problem as there is only one project type.
Updated March 20, 2014