This is a common problem (so I've found out) but I cannot get WP to play nice with IIS 7.5 / PHP 5.6. Updating (WP + plugins) and installing (plugins) always return the error "Cannot create directory".
I am not using (nor can I use) FTP. The folders, include the temp folder all have full read/write access for the application pool identity and IUSR / IIS_IUSRS. I have tried all combinations of permissions and app pool identities to the point of exhaustion. I do not have Windows Cache Extension installed. I've tried this - How to update Wordpress installed on IIS? - I've even tried setting the app pool and site security to be the admin account on the server!!
What I'm looking for (very hopefully) is that single nugget of information, something to try, that I haven't found in the 3-4 days of Googling and messing around that I've done. I really hope somebody can help!!