1. the paper from which the modules were folded was too soft,
2. I wasn't patient enough, so I started to assemble the model before all units were folded,
3. I thought, being a semi-mathematician and relying on my good logical skills, that it will be easy to figure out the proper three-colouring of the ball (the proper colouring means that no two units of the same colours are next to each other).
So I was in the middle of assembling when I realised that I have made a mistake with colouring and that I cannot figure it out as easily as I anticipated. To solve this problem, I sent a question to ever-reliable O-list and after some time got several replies. I even received an email from Mr. Hull himself, which was WOW! He sent me a paper with explanations on how to construct buckyballs and how to three-colour them.
Unfortunately, by the time I received these emails and found time to made missing modules and to continue with assembling the ball irreparably lost its shape because the soft paper was not able to support the weight. I cannot describe how frustrating this was! I was disappointed, dispirited and in the end very angry so that the poor ball ended up in the trash can instead of being proudly presented to a friend of mine as a gift for receiving his master's diploma.
After I had cooled down, not being a quitter, I decided to learn from my mistakes and to start over. This time I used copy/printing paper which is much more rigid. It took me ages to make the ball because I was not in the mood to cut 270 squares. This year I decided to finally finish the project, done what was left of the cutting, folded all modules and the assembled them. this time I was better prepared, ready to be infinitely patient and my effort was rewarded. It took some musing and brain stretching until three-colouring algorithm was clear to me, but then everything went smoothly.
I think that the final result is more than rewarding. The ball looks fantastic and I am so proud to have finished it after all.