Which Version of PCLinuxOS are you using? KDE, XFCE, or other?
Try to give as much information as possible when asking questions. That way you will have a much better chance of getting and answer that will actually help you. for instance Taskbar keeps slipping doesn't really tell us anything about what is happening. What do you mean by slipping?
I downloaded the latest xfce version last wednesday
I just looked in the system settings and suddenly the taskbar was vertical on the left, I'll post a screenshot?
How can I move the taskbar horizontally to the top?
in that case right click on a black space on the panel a dialogue box will come up go to panel the panel preferences and there will be a box there that say vertical or deskbar click on it and select horizontal. That should fix it for you. After you do that you may want to check the box that says lock panel. Good luck.