Enough talk. The first problem I will discuss is one that bother many users. Once in a while an app would fail to be updated (installed) no matter how hard you try. The Android Market may give you an unknown error of reason -18. Some people encountered this problem after Market tried to silently update their apps but failed. One common example is the popular game Angry Birds (and all its variants.)
AFAIK, the problem has something to do with your SD card. You might find many different ways to fix it online, but some of the solution may be too technical for some people. So, here's an easy fix.
- Launch the Settings app
- Click on Storage
- Under SD Card, choose Unmount SD Card
- Once the card is unmount, go back to your launcher and launch Market
- Choose to re-install the app that's giving you the problem
- Your app should be installed now