[Delete Unassociated Items suggestions]

Thank you very much, your suggestion was very useful. I removed in few clicks a lot of unassociated items.

[Rigged mesh makes my av disappear when worn?!?!?]

Have you tried to Reset Xform the boxes before apply the skin?

[Why does the "Calculate" button vanish for rigged import?]

This issue happens because some of the bones are not included in the rig, the official SL viewer need all the main 26 bones listed in the Collada file to work properly, even if you use some of them.

You shoud open the Collada .dae files with a text editor, and search for a string like this:

<Name_array id="Object_01Controller-Joints-array" count="26">

If the count value is different, you modify it to 26. After that you should check the bones list:

mPelvis mHipLeft mHipRight mNeck mHead mChest mSkull mEyeRight mTorso mKneeRight
mCollarRight mCollarLeft mElbowRight mWristRight mShoulderRight mAnkleRight mFootRight mToeRight
mEyeLeft mKneeLeft mElbowLeft mWristLeft mShoulderLeft mAnkleLeft mFootLeft mToeLeft</Name_array>

If some bones of the above list are missing you should add them between your listed bones and the </Name_array>, save the .dae file and import it on SL, if everything is all right the "Calculate uploade weight & fee" button should remain enabled.