Blossom drop is common early in the season. The number one cause is that temperatures are not yet quite right. Like tomatoes, if it is too cool or too hot fruit will not set. Capsicums like night time temps to be above about 16 C for fruit set. Also if daytime temps are too high (above about 35) fruit will not set. There is probably minor variation among varieties in the actual optimal temperature range, but you get the idea...Generally patience is the only remedy required. Other possible causes are not enough airflow (capsicums are primarily wind pollinated), too much nitrogen, not enough water, too much water...

- Tracey