The most common reason for a recognition timeout is slow network speed, particularly if you are not on a 3G network. The ideal situation is to connect to a WiFi network, but that's not always possible. If you're not using WiFi, check your network signal strength in the upper left hand corner of your iPhone. Vlingo will work best if you have at least 3 bars of coverage.
Occasionally Vlingo will time out even with a strong network connection. This is less common, but may occur if you spoke for a particularly long time or if Vlingo is having a difficult time understanding what you spoke. You can also experiment with speaking fewer sentences at a time. You can always break your messages into multiple chunks. Once Vlingo has inserted some text onto the screen, just position the cursor wherever you want the additional text to be inserted, then speak again to insert it.