Hi,

the output folder of my Mesh Helper contains this:

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When I upload the .dae file the texture is missing.
I checked "texture included" at the upload menue.
Does anybody know why?

Greetings

Yes, Second life does not allow you to upload rigged mesh with textures, Ever ever ever.. only static meshes can be uploaded with textures
Pretty sure I said that in the tutorial for this, but its whateves.
You'll have to manually add the texture to your mesh

You can use TexFix from tools to texture your mesh

what i see you have the uuid numbers 
add them to your clothing,
change your textures add the uuid number