Version depandabiliy – I don’t know why but I was using wordpress 3.3.1 and suddenly one day these function stop working I don’ know why ? but that’s the same thing happens to me – I usually install some common plugins to all my sites – but I never knew if i was plugin fault or update fault – once I upgraded to 3.5.1 these error automatically vanished. Might help us detect if you list your plugins ? do you try deactivating and then checking ? if not the best solution worked for me is upgrade – if you are up to date and using wordpress 3.5.1 and didn’t detect any conflicting plugin causing this problem then – try downloading your theme’s from your hosting control center and overwrite the current wordpress with the new one or re-install the wordpress. upload your theme and connect your old data base every thing remain same but might help you finishing the problem.
Some time I observed in my career that some things once changed will bug you until you re0install them completely, there are certain coding that over write the orignal wp-files or might be posible a virus or malware over write them – and your hosting authories – scan and removed the malware but the website main core files are still infected or modified causing this problem and you are just puzzled thinking what’s wrong with your plugin.
Although this step of re-installing wordpress should consider as the final step if you don’t get any legtimate answer to counter the problem. while please Keep us up to date.