google play store - Apps won't install (silently fail after 100% downloaded)

I have a problem with installing apps from Google Play onto my Samsung Galaxy S Plus phone.

It has Android 2.3.6. Yesterday I tried to download some apps. When I clicked 'Install', the app began to download but when it got to 100% it just disappeared and silently failed to install on my phone :\

I don't have an SD card and up to now I saved all my apps on the phone and had no problems like this. It seems to be some settings problem, but I don't know what to do. any ideas?!