camera card readers limitation

Have had problems reading SD cards on slot on my PC… so acquired an external USB multitype card reader which copes with most SD cards .. but I now have a 2gb card wgich sometimes is read succesfully and sometimes only reads some of the files.
I have read that there is a capacity limit on these card readers (I presume a buffer limitation?) can any one offer any information and how to download from the higher capacity cards that are now in use?