For me, the problem is in the upload facility inside the image properties.  I am using v1.0.4 with DNN 4.3.3, and I'm logged in as myself (i.e. as a member of the administrators group, but not *the* admin user).

---

1) What is the exact name of the file being uploaded? and the size?

The exact name of the file is "setup-banner.jpg".  Its just a file I chose at random to reproduce nhgile's issue.  It's a 22KB file.  I tried it on a different image, same problem.  The error comes up immediately - not enough time for it to actually attempt a postback.  The message is being generated client-side.

2) can you write here the string content of the error message

The error text is "Security error. You probably don't have enough permissions to upload. Please check your server." It's a popup message box.

3) Do you have this error using all instances of the provider? or it is a problem with only one module?. Can you check that if you are not sure?  4) Do you have custom attributes applied to that provider instance? if the answer is yes, can you post your customizations here?

I tested it on a random text/html module in my live portal.  I just tried it on another module, same issue.  No custom attributes.

 

---

I had the same error, the way it got fixed was by simply login in again as host, for some reason I think that dotnetnuke has refresh itself every time a new process is executed to fully implement it.