As noted above the 9900 only supports 32GB.
Also as noted it is always a good idea to back up the memory card periodically by connecting to your computer and saving the memory card contents on your computer.
Kingston is a well recognized relaible brand for computer memory. As with BlackBerry batteries selling at half price to those in known shops, cheep memory from ebay might be suspect. I don't think I have ever seen Class 3 memory. class 4 is the lowest I have seen.
However, I think the main issue is you are trying to use a 64GB card in a device which will only recognize 32GB.
I have a 32GB class 10 in mine with no problems.
One tip: As with camera memory, it is often recomended to format the memory card as soon as it is first put in the BlackBerry so that you know that the memory card format is totally compatable with the device that it is in. I am told that there are subtle differences in fromatting and that while the generic formatting of the memory card done by the manufacturer will work 99% of the time, it is better to have the memory card formated by the device it is acutually in to be totally compatible with it.
Here are instructions on how to format your micro sdcard.
Format your media card or built-in media storage - BlackBerry Bold 9900/9930 Smartphones - User Guide - BlackBerry Bold Series - 7.0