I just wanted to drop a quick post on here in case anyone else is running into this issue (and to remind myself of the solution when I forget it).
I wanted to make a 3D print of my school district logo on my Polar3D printer. I brought the PNG file into Illustrator and manipulated it as needed. Then I exported as SVG. The problem was that particular SVG file would not import into Tinkercad. The file type wasn’t wasn’t recognized.
The fix is pretty simple.
The SVG file is actually an XML file but when Illustrator creates it, it doesn’t add the first line of code to the file that specifies it is an XML file. So, the fix is to open the SVG file in your text editor of choice (Dreamweaver is mine) and add the following at the start of the file.