1) I was using 7.x-1.0-beta4 which worked fine except for this issue: http://drupal.org/node/1239946
2) I upgraded to 7.x-1.0-beta5 and got WSOD when viewing any node with a field collection, although I was able to edit the nodes OK. (i.e. I could go into "edit" and view the submit form, but not save the changes)
3) I installed 7.x-1.0-beta4+11-dev which I had working on another site (I installed this version to solve the issue mentioned in point 1) but this time when trying to submit edits to a node I got "The website encountered an unexpected error. Please try again later" - but I could view the node OK this time.
4) I reverted to 7.x-1.0-beta4 but on running the update script I got "Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 30720 bytes) in /modules/system/system.admin.inc on line 2078". After a few tries I got out of that, and now I can view and edit nodes OK but when submitting my changes I get "The website encountered an unexpected error. Please try again later."
5) all of this happens only to nodes with field collections
6) I cleared cache several times and did run the update script between each successive update of the module
7) possibly worth noting that when editing the nodes, I was sometimes deleting the extra empty field collection that the system added automatically before saving the node, but even when I left the empty field collection in place and then saved I got the same results.
8) if I now try and add a whole new node with a field collection I get "The website encountered an unexpected error. Please try again later." and on checking back under /admin/content the node has not been saved.
9) I am using Entity API 7.x-1.0-rc3