Autodesk Inventor

[#1]

I'm at my wits end with this error below during weldment of 2 pieces of mild steel - a backing plate...nothing spectacular:

• Create Weld Feature: problems encountered while executing this command.
•      Trolley Base Assembly Weldment.iam: Errors occurred during update
•         Weld Compute Failed due to a modeling error
•           Fillet Weld 19: Could not build this Fillet Weld feature
•             Weld Compute Failed due to a modeling error
•               The Weld Bead operation did not produce a meaningful result. Try with different inputs.

I've changed the weld size, even though there is ample space for the weld, tried applying the weld a bit at a time but it keeps failing. I can place a weld along some parts but I then have spaces which is not what I'm after. As I pick the surfaces to weld the proposed weld is shown until I pick a surface where it then dissappears...

What am I doing wrong and is there any good tutorial on weldments in Inventor?  I need help... currently with weldments in inventor and probably psychiatric in the near future if I don't get my head round this problem!

[#2]

Attach the files here.