I imported an .ai file into Inkscape 0.46, and used only a part of it, I needed the head of the character, and the rest of the image I made by myself with Inkscape. I noticed some things that are way wrong, and that are maybe the reason I can't import the derived .svg file into Illustrator. I know this is already mentioned, but this case is different. Here are the facts:

I got a file from the client in .ai format. My company just started, and we still did not buy Adobe Designer Suite, so there is no Adobe Illustrator on our system to re-save the file as .svg from Illustrator.

I imported the AI into Inkscape, removed the part that I don't need, and everything looked good, there were some warnings about gradient meshes, and replicating them, but everything looked right as it should. Right until I clicked on an object and I saw that it's fill and stroke settings say "undefined". I guess that's wrong...I spent an hour replicating the gradients and hand-picking the colors, just to remove the "undefined" from all imported objects. When I did that I saved as plain svg and sent to a friend to try to open in in Illustrator, import, place, whatever...just to read it. He reported the file crashed Illustrator on import, and couldn't place it because some error. I tried with few more friends, all having different versions of Illustrator, with no success, either the file crashed AI or AI couldn't import...

I paid attention not to use blur, transparent gradients, I only used opacity on a few objects that I need to be transparent. I can't get why Illustrator won't import/place file, because I already imported my Inkscape artwork in illustrator earlier and I am aware of compatibility issues. I could export to EPS, but I need that transparency, which I can't have with eps.

Here is the file, can someone please try to find what's wrong with it...
http://www.humyo.com/F/884647-187294031

And can someone tell me what is that "undefined" problem caused by? And do you get the same when you import AI?

There is clearly a bug in Illustrator (even if the file is incorrect, Illustrator shouldn't crash). Have you tried asking about it on an Illustrator forum?

I can't see any problem with the SVG file you provided. Is this the file before or after you "fixed" the undefined fill and stroke?

Right until I clicked on an object and I saw that it's fill and stroke settings say "undefined". I guess that's wrong...

Not necessarily. If it's displaying correctly, then it's probably OK. The fill and stroke may be defined at a different level than you're looking at.

I concur with sas. It doesn't matter what is in that SVG file (valid or not), if it crashes Illustrator then there is a bug with Illustrator. Illustrator should either ignore what it doesn't understand, or display a message if it's beyond recognition.

The guys over at IllustratorWorld.com are pretty helpful.