In general project operation information of each class and there is no error in the operation but will appear errors exist in required project.
And sometimes run will be successful. This situation is due to problems in the other project categories not address the root causes affect the overall operation of the project.
Another case is the class did not have any problems but there is an exclamation point and the like before the project, in this case may be due to the package is not imported correctly.
Here are solutions.
1, there is an exclamation point before the project or x No.
2, open the build path right build path selected the configure
3, as shown in the wrong bag delete re-import the package they need
4, and then compiled to refresh.
