This happened just after I selected album art from the "search online for picture" results.
MusicBee v3.0.6335.15398 (Win10.0), 14 Jun 2017 16:45:
System.ArgumentException: An item with the same key has already been added.
at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
at #=qz0DJW_iqhyi8DxNfTD84LpLObItY14ZeCnajGbhqxoE=.#=qPxYBg5_rBDBmZCNEblzDopQaXBm9xqyH2XgDVdvghU4=.#=qa7bBzUTE6rPlig5K03pIw380IrYauWSiGfCJcbBsLKE=(IEnumerable`1 #=qM58enh59F3dyKYh9CHCSXQ==)
at #=qZ_oqWt4xZNzELo2RyzTcrpZttdvBvBz9qNs5Wf7cz7s=.#=q21FxIXnHC_nDxry7Q0bGxnLBbcQT_v9vsl50KQi73DI=.#=qqr78GRL$A6k$fRv7lV8Png==(IList`1 #=q4c_O4v9_JMBhzVskFc9HUg==, Boolean #=qafNL6QcKBcE1IkTWOazjtQ==)
at #=qZ_oqWt4xZNzELo2RyzTcrpZttdvBvBz9qNs5Wf7cz7s=.#=qkbLE$1YlMTNfoiT9dWv1sg==(IList`1 #=qlgJBkwY9HTR0mu$8bmtHeQ==, TagCode #=q41QTucsKk2skirHKOpIUQg==)
at MusicBee.MusicBeeMain.#=qkbLE$1YlMTNfoiT9dWv1sg==(IList`1 #=qNovCnsvGta6SFUkyKDuPlw==, TagCode #=qCmd3it7QjATAoeXlH7NEPQ==, Boolean #=q6g88o2$WXrOlOnLSZbKi_6iQsqxw0cor3nIyVSdaL6s=)
at MusicBee.MusicBeeApplication.#=qb1m_xtPp4p$RBhGPLgqcfxv258NprYkU_aS8n7UCwF8=(IList`1 #=qELHnuDA4XeeZ$kq5SQA_sg==, TagCode #=qgmB91PC3nO5ecwtaho2XhA==, Boolean #=qyI$H$tC2t_IEyINHFNRCbAtKB52TYPmuU62oDvap96Q=)
at #=qCBOUNiPC0oh1bLzYn4sKbi3EZmliorXXSwmMTfWXT_1kAgFvsbZKKCRW$m_DagJr.#=qtelXEbWgUQRl7z0MZi9Bp5ka$45kgOdaJLVXdZto0p0=._Lambda$__0()