Most likely the server is blocking the cURL connection to the webassist server.
see this post for a curl test script that will test the connection top the webassist server:
read write permission is needed on the webassist directory for the design editor to function.
it is also needed on the imagesupload directory that is used by the file manager in the content management section and for uploading product images. Without write permissions, product images would not be able to be uploaded.