Trust that you are doing great!
To solve this issue you have to correct the xml file before loading into QlikView application (refer below draft version of xml file):
<tasks> <task> <key>documents/de/oxx?mmsArtNo=333993&variantNo=1&bundleNo=1&language=de</key> <content>INSERT</content> </task> </tasks>
Hope this will be helpful.
P.S.: Place a semicolon after &.