What problems occur during painting?

It depends on what you are painting. In general, if it is possible to have a problem, you will! Most problems occur, I believe because people fail to read the instructions, do the prep work, which is the hardest, most time consuming and boring part of the job, and use the wrong paint for the project. Like anything you do, having the right tools for the job, and taking the time needed to get everything ready to be painted is the best insurance against problems. If you do not have experience painting, talk to a specialist in the paint department of a good hardware store. Sometimes the big warehouse stores don't have employees that can give you good advice. There are certain ways you need to cut out the room, certain techniques for rolling on the paint, different types of roller pads for different surfaces. You use a semi-gloss to paint wood trim but wouldn't want that on the wall. Conversely, you usually paint living and bedrooms with a flat latex but would not use flat paint on the trim.

Finally, don't start any painting project until you have everything you need in place, all the prep is done, and that you are sure to have plenty of time to finish what you start.