The quintessential premise on the basis of which every technology in the world is created is to reduce mechanical work by a human. However, that technology is not 100% foolproof and can often contain glitches which can hamper work. The easiest example that comes to mind is the Beta version of a new Microsoft Windows. It is the same case with automated testing in software.
Automated testing increases the speed of testing. It reduces labour costs since the process can go on even when a human is not present. But then, it is not as thorough as manual testing.
Problems encountered in automation testing
1. Unnaturally high expectations
It is normal to expect that automation will get rid of challenges faced due to manual testing. Vendors often harp about benefits of this process, and downplay the amount of effort needed to obtain the same. General optimism from automation is expected, but not optimism that points towards sky high expectations. So have reasonable expectations from automation.
2. Participating in poor testing practices
In case the testing practice is poor, where tests are poorly organised with inconsistent documentation and if tests are not effective in pointing out defects, then there is no point in automation. Therefore you need to improve your current testing practices.
3. Technical problems related to tools
The commercial test execution tools are sold by vendor companies, and are not completely immune to defects. Problems with third party products or your own applications can always crop up. You must give it the time necessary to solve such problems.
4. Expecting that automated tests will find several new defects
When the test is run for the first time, it is likely to find defects. But if it has run and already passed the test, no new defects will be found. So do not run the tests unnecessarily in the hope of finding new defects.