This is not an uncommon problem with WordPress plugin installs as a quick search of the WP support forums will show.

It can sometimes happen, I am informed, if the plugin zip is unzipped within the plugin folder. But I am unsure what the actual cause it. I can tell you the plugin does have a valid header!

You will need to remove whatever id there. So in the WordPress 'plugins' folder remove the simple-press folder completely. The have another go. If it fails again you may need to unzip it locally and ftp the folder up to the server. 

Or you could take a look at the WP forums which, as I say, have a lot of questions on this one. There may be a better answer buried in there somewhere! But using ftp might be quicker 🙂

It is a little problem we never really understood. WordPress developer recommendations propose that all functions written in a plugin be prefixed by a unique identifier to avoid collision. So - being named Simple:Press we prefix all of our functions with 'sp' and one such  function is named 'sp_get_option'.

For some reason the Event Calendar plugin also has a function named 'sp_get_option' hence the conflict. I thought I was told a while back that they had changed theirs but if your EC plugin is up to date then I guess this was not accurate.

It does, sadly, make it impossible to have both plugins installed on a site. We really can not change it that easily without disturbing existing users - m,any of whom have added custom code to their forums.