Issue Solved
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I kept researching about this — given that I could run (and upgrade) version 2.4 on my other Mac system and various test Windows systems I did not think that it was likely to be OpenLP 2.4 code.
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I didn't think it was the computer either as it has same version of OS X as the other Mac and the machine was running perfectly and hardware tests showed no issues. The reported crash cause being a segmentation fault 11 was an indication, but also somewhat misleading, as it gave the impression of an issue with the running code.
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After a lot of Google searches I started to think it could be down to the OS X '.plist' preferences files as I saw reports of segmentation faults due to problems with .plist files.
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In my ~/Library/Preferences folder I found two .plist files
org.openlp.plist<br>
org.openlp.OpenLP.plist<br>
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I removed both of those, made sure the previous system data folder was in <font face="Arial, Verdana" size="2">~/Library/Application Support/openlp/Data so that databases would be upgraded, and </font>started version 2.4 — and it was fine. I had to redo all my configuration settings but that was not much work.
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I did notice though that in the ~/Library/Preferences folder there is now only the org.openlp.OpenLP.plist file. Where the other one came from (a previous version at some stage?) I don't know. Perhaps one of <font face="Arial, Verdana" size="2">the</font> developers can shed light on this and confirm <font face="Arial, Verdana" size="2">that the only .plist file used now is org.openlp.OpenLP.plist.</font>