Have done reviews for IEEE, APEC, and ACM stuff. There can be many reasons that a presentation is not accepted. Some rejects are a simple instance of subject matter not matching the scope of the symposium. Or there can be some problems with the math and other technical issues. Another unfortunate and not uncomman issue is where the English syntax and/or grammar is so poor that the meaning of the proposal is lost. And there can be the occasional submittal that is a bit before its time - it has happened to myself. Example is the IEEE (PSES and other societies) is probably at least 15 years behind the ACM on matters of software safety and test methodology. Members of the ISPCE tech committiee recently approached me about a session on software safety analysis for the 2017 symposium; yet my submittals for similar presentations were rejected at least twice during last 10 years, by this same group of people.

So a rejected presentation proposal may not have necessarly been a poor idea. Please do not take rejections personnaly.