I can't open some of my Apps!

If you've done a hard reset (hold HOME and SLEEP until an Apple logo apprears, do not Slide to Power Off) and the phone is not jailbroken connect you your computer, go to the Apps tab and uncheck all of the apps, then sync to remove them from your phone. Then repeat, this time checking the apps to add them back.

Hello,
If reseting the iphone still doesn't help you will want to double-click the home button and you'll see the display shift upward and a row of your app icons on the bottom, gently place your finger on one and hold until they dance, and a red ball with a white minus appear tap the minus until all of the apps are gone then press the home button once again this will clear all of your recently ran or running apps. Multitasking in iOS 4.xx the apps will NOT be deleted just stopped and cleared out of memory. This will correct the issue.

Was really getting frantic with my apps "crashing", a hard reset didn't work, so followed whta you suggested and Hey Presto!! they now work!

Many, many thanks, it's saved me a journey to my not so near iStore.