Well, where did you find this message?
Typically, when you build your app, Xcode runs a series of build tasks, such as invoking the compiler and linker. Typically, each task is handled by a command-line tool, and if the tool detects an error it exits with an error code. Sometimes, the tool put a generic message like "Task failed with exit 1" in the log, which just means it didn't succeed. Typically, this is preceded in the log by some more useful message, detailing what went wrong.
To find this useful message, look in the build transcript (Command-9). In the navigator pane on the list, click on the build that has an error icon (the topmost, or most recent, if there is more than one), then select the specific step with the error icon in the editor pane. Over on the right, you'll see an icon made up of several horizontal lines. Click it to reveal the build transcript for this step. Near the end, you should see any any error messages.
Is that any help?