Welcome to SolidWorks forums Fred.
You should be able to open the DWG file directly in SW instead of importing and into a part or drawing environment (you'll be prompted for that when you open the DWG file). After that you should be able to extrude them.
If you still see the error then while in sketch mode go to Tools > Sketch Tools and click on Check Sketch for feature. Pick the extrude feature from the pop up window and SW will find the issue for you. What I feel is that there is some extra tiny line somewhere.
If still the error is there then post your file here.
Please use "advanced editor" in case you want to attach any files.Click on reply and then click "use advanced editor".
You might also find this post helpful for your future reference.
Many thanks for your helpful reply. I followed through with the suggestions that you made. When I attempt to extrude the outline I receive a message indicating 'the sketch contains an open contour'. I then followed through with your suggestion of making use of the 'check sketch for feature' option. When I come to the small 'repair sketch' window, it indicates 'no problem found'.
I notice that when I select 'extrude' a FAINT tick appears in the small box located to the left of 'thin feature' on the RHS of the screen. I cannot remove this tick - and as indicated, it is only quite faint, which is presumably indicating that the thin feature is the only extrude option that is possible with this sketch. I suppose this makes sense if the sketch contains an open contour.
I've been through the process quite a number of times to try to make sense of what's happening - I'm sure that it's something really obvious that I'm missing.
I've reduced my input diagram to something that is very simple in order to try to sort out the difficulty. Attached is the .dwg file that I generated using live trace in AI, and also the very simple test scan that I used as the input to AI. Very many thanks if you're able to help with this.
Hi Deepak, Mark, many thanks for your help with this. Clearly I had not zoomed in sufficiently, so I missed the connectivity problem.
I'm using the current student edition of SolidWorks. Yes I see what you mean - now I see that in SolidWorks it's possible to directly open an AI file, which is most helpful.
The process is now working really well and I've been able to 3D print some of my components.
Have you tried to open the Illustrator file (.ai) directly into SolidWorks? What version of SW do you have?
(there were changes made to this functionality in 2010) If you do this you can open the Illustrator file direclty into a sketch.