Wikimedia Bugzilla is closed!

Yes, this seems like a bug. I permanently get this error too with a hand written svg file containing valid svg code as checked by the w3c validator as well as by Jarry1250's SVG Check. I found similar questions at Commons:Help desk/Archive but no solution. I studied a dozen of Bugzilla's threads, removed the <Title> tag and have no nested <g> (Bug 4388).

Can somebody at WMF run MimeMagic::singleton()->guessMimeType() on that file?

Here is the code:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">

<svg version="1.1" xmlns="http://www.w3.org/2000/svg" 
 viewBox="0 0 800 500" width="100%" height="100%" >

 <defs>
    <marker id="Arrow"
      viewBox="0 0 5 4" refX="3" refY="2" 
      markerWidth="5"  markerHeight="4"
      orient="auto">
      <path d="M1 2L0 0L5 2L0 4z" />
    </marker>
    <linearGradient id="Gradient" gradientUnits="userSpaceOnUse"
                    x1="0" y1="0" x2="800" y2="0">
      <stop offset="0"   stop-color="white" stop-opacity="0" />
      <stop offset=".06" stop-color="white" stop-opacity="0" />
      <stop offset=".09" stop-color="white" stop-opacity="1" />
      <stop offset=".94" stop-color="white" stop-opacity="1" />
      <stop offset=".97" stop-color="white" stop-opacity="0" />
      <stop offset="1"   stop-color="white" stop-opacity="0" />
    </linearGradient>
    <mask id="Mask" maskUnits="userSpaceOnUse"
          x="0" y="0" width="800" height="500">
      <rect x="0" y="0" width="800" height="500" fill="url(#Gradient)"  />
    </mask>
	<symbol id="trace">
		<path fill="none" stroke-width="4"  d="M-50 260L100 400L400 120L700 400L1000 120"/>
	</symbol>
 </defs>
 
 <path d="M40 466V 20" stroke="black" stroke-width="3" marker-end="url(#Arrow)" stroke-linecap="square" />
 <path d="M40 466H780" stroke="black" stroke-width="3" marker-end="url(#Arrow)" />
 <text x= "15" y= "60" style="font-size:24px">f</text>
 <text x="740" y="490" style="font-size:24px">t</text>
 <g mask="url(#Mask)" >
  <use stroke="#aaf" xlink:href="#trace" x="-10" y=" 0"  />
  <use stroke="#ddd" xlink:href="#trace" x=" 50" y=" 0"  />
  <use stroke="#faa" xlink:href="#trace" x=" 50" y="-80" />
 </g>
 <path d="M 50 420h 36" stroke="black" stroke-width="2" marker-end="url(#Arrow)" />
 <path d="M190 420h-36" stroke="black" stroke-width="2" marker-end="url(#Arrow)" />
 <text x="120" y="420" text-anchor="middle" baseline-shift="-30%" style="font-size:24px">&#916;t</text>

 <path d="M320 120h145" stroke="black" stroke-width="2" />
 <path d="M320  40h145" stroke="black" stroke-width="2" />
 <text x="320" y="80" baseline-shift="-30%" style="font-size:24px">&#916;f<tspan style="baseline-shift:sub;font-size:0.85em">D</tspan></text>

 <path d="M250 190v33"  stroke="black" stroke-width="2" marker-end="url(#Arrow)" />
 <path d="M250 287v-33" stroke="black" stroke-width="2" marker-end="url(#Arrow)" />
 <text x="180" y="210" style="font-size:24px">&#916;f<tspan style="baseline-shift:sub;font-size:0.85em">auf</tspan></text>

 <path d="M550  96v33"  stroke="black" stroke-width="2" marker-end="url(#Arrow)" />
 <path d="M550 306v-33" stroke="black" stroke-width="2" marker-end="url(#Arrow)" />
 <text x="535" y="200" style="font-size:24px">&#916;f<tspan style="baseline-shift:sub;font-size:0.85em">ab</tspan></text>
</svg>

Just tried the file in  comment #0 and that one is actually uploading without any problems.

Closing WORKSFORME for comment #0

Comment #3 hits bug 27544; the file is actually not valid XML; if I load it with Firefox it gives "XML Parsing Error: prefix not bound to a namespace"

Thank you for the hint at the namespace; xlink was missing.

Thank you for the hint at bug 27544; I reopened it for the mere reason to urge the developers to make the error messages more informative.