Using multiple Templates per section
You need to allow the entry.type value to be part of the include path...

{% include "events/_types/" ~ entry.type %}


Since your entry.type is "summerpreview", that will be parsed out like this...

{% include "events/_types/summerpreview" %}


With Craft, you don't need to specify the .html extension, so this include should work perfectly.



As a side note... I'd recommend turning on devMode locally. It would have thrown an error, telling you that summerpreview is not a legitimate variable.


  What Dev Mode Does