vba - Dreaded "Excel found unreadable content in..." message after adding custom icons -

i've been working on excel addin makes use of ribbon. fine until attempt add custom 16 x 16 icons. here in office, have excel 2007, is

microsoft office excel 2007 (12.0.6683.5002) sp3 mso (12.0.6683.5000)

my winzip is

winzip 15.0 (9334)

when open .xlam file zip file, have customui\_rels , customui\images subdirectories. contents of customui.xml.rels file is

<?xml version="1.0" encoding="utf-8" standalone="yes"?> <relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"> <relationship id="nbinsert" type="http://schemas.openxmlformats.org/officedocument/2006/relationships/image" target="images/nbinsert.png" /> <relationship id="nbchange" type="http://schemas.openxmlformats.org/officedocument/2006/relationships/image" target="images/nbchange.png" /> <relationship id="nbdelete" type="http://schemas.openxmlformats.org/officedocument/2006/relationships/image" target="images/nbdelete.png" /> </relationships> 

the companion customui\images subdirectory empty.

at stage, file opens correctly. main customui.xml not reference these new icons. relevant part looks this:

  <box id="box01b" boxstyle="horizontal">     <button id="bb00" onaction="nb.wrchange" imagemso="changebinding"       getscreentip="nb.wrchangescreentip" getsupertip="nb.wrchangesupertip" />      <button id="bb01" onaction="nb.wrinsert" imagemso="recurrenceedit"       getscreentip="nb.wrinsertscreentip" getsupertip="nb.wrinsertsupertip" />     <button id="bb02" onaction="nb.wrdelete" imagemso="cancelrequest"        getscreentip="nb.wrdeletescreentip" getsupertip="nb.wrdeletesupertip" />   </box> 

i not use custom ui editor, xml either hand coded or generated.

once icons in, have change, example imagemso="changebinding" image="nbchange". @ least, that's have hoped.

then copy new icons, 3 .png files, images subdirectory , save , rename .xlam file. when attempts open addin, excel complains aforementioned error message. consequently, after remove these offending icons, addin opens correctly.

in word 2010, had no problems having extra, unreferenced icons hanging around in images subdirectory. also, references nonexistent icons in xml resulted in icons not displaying, never error.

is there special custom icons needs observed them work, example, no transparency? or addin file fragile , sensitive? or should try later winzip version?

these icons found on www.iconfinder.com made smaller (originally 32 x 32, reduced 16 x 16) using ms paint. tried changing them 24 colour .bmp icons , had same problem.

i had custom icons in excel 2010 (copied same place, 32 x 32) worked without fuss.

any suggestions welcome.