suzan19,
I don't know what your problem could be, but I would try "clear data" anything related to the market app or google. Note that you will lose your settings for those apps. Also make sure you have the correct version of the market for your phone. Try reading over previous posts in this thread, maybe something will help you.
Jabzzzz,
To paste you select the paste option in the file explorer. Maybe you mean that it gives you an error? Maybe you did not root your phone properly -OR- you are suffering what lillalioness wrote only 2 posts above yours! In fact, I think that lillalioness describes the exact problem you have to which he wrote a detailed solution.
lillalioness,
Thank you for your explanation.
Everyone,
If you are having problems. Re-read the how-to and make sure you did not miss any detail. Read it slow. If you are still having problems, keep reading what others say. There are a lot of really helpful replies here with solutions, read them!
Happy hacking and have fun. I should say that Xperia X10 Mini no longer receives updates from SE, so the solutions here should work for everyone. From the time I wrote the how-to the market has been working without a problem for me throughout all the updates. I no longer use the X10 Mini so it's also hard for me to diagnose problems people are having. But like I said, a lot of people have offered solutions to problems, so read all the replies.