I simply have a web api application on IIS server that simply writes to text file on C:\\FileStorage\\test.txt however when I call this webservice I get the internal 500 err
Grant permissions for that folder to the application pool. So you'd go to the C:\FileStorage folder in Windows and edit permissions, and add IIS APPPOOL\appPoolNameHere as a user, then give it full permissions.
Hope that helps.
EDIT
Step by Step Instructions...
-Open Windows Explorer
-Browse to your folder
-Right click the folder and go to Properties
-On the Security tab click Edit
-Click Add
-Under Locations, make sure it is pointing at your local machine, not a domain
-For the object name, enter below but replace MyAppPool with the name of your application pool...
IIS APPPOOL\MyAppPool
-Set the permissions to Full, or just add Write, or whatever you need.
or you can repalce APPPOOL to the name of your server or computer and with the IIS_ISURS.
example:
yourserver\IIS_IUSRS
See this Screen Shot
