How to get an application back on the purchases page after deleting it

Hi All,

I bought OS X Mountain Lion on the App Store and while trying to reinstall all softwares after experiencing somes crashes, Montain Lion report an error.

After many attempts, I could not reinstall due to an error, so I deleted it from my purchases pages and now the App Store will not give me an option to buy (even again) the OS X Montain Lion. Please advise.

Most of my others softares run on Mountain Lion, and until I sort this out, I can not work.

Yours sincerely.