I assume you burnt the RW as if it was a “normal” DVD, this meaning not using packet burning software like InCD but Nero Burning Rom, Nero Express or a software to produce slideshows.
Compatibility probs are less frequent nowadays but still can happen, and as you say you can play it but a number of other players can’t it may be or not be a problem of the media you used.
Are you sure the other players can use DVD+RW discs?
Are those players PC drives or home players?
How did you burn the slide show? As a data disc or as a DVD video?
The best way to improve compatibility would be to burn the slideshow as video so the the player see it as a DVD-video, using a DVD-R or a DVD+R disc.
And if you use a DVD+R to use bit setting as a way for the player to “see” is as a commercial DVD-video disc. By the way, if your drive/software allow it you can also apply bit setting to a DVD+RW.
Nevertheless, using good media it is a good idea (besides I didn’t have bad experiences with Memorex media, but when it comes to DVD+RW I had problems using packet writting software - in the case InCD - that would not allow neither further writting to disc nor reading it, and this with other good brands of discs, including Verbatim).