If using .NET resizer plug-in in v3.1 or selected ASP.NET resizing method in v3.15/3.2c/3.3/4.0, then the problem with uploading images relate to ASP.NET configuration. Make sure the account, which handles .NET applications (usually "NETWORK" or "NETWORK SERVICE" or "IWAM_...") assigned "Modify
permission to "cl_upload
folder. There is also a chance that ASP.NET is not properly configured and installed at web server. Consult hosting support and online hosting documentation.
Note: The ASP.NET must be properly installed and configured at your web site. If you receive the "Server Error in '/' Application", "Service is not Available", "Service is not properly configured", "Configuration Error" after you assigned appropriate permissions to "cl_upload" folder, then you need to apply to your hosting support for resolution.