I'd like to recommend creating a account so me or other members can assist you, as guest have limitations in replying here and if we need further Information to communicate with you.
Is is saying "your memory card", or "your memory"? If there's not enough free space internally, some apps can't run. (Since Gallery shouldn't be looking around in storage [it looks in the Media database], you shouldn't get that message - unless it's not referring to storage, but to memory - RAM. In which case, just restart the phone, then run Gallery.)