When I try to upload a new skin for my site I get following error message, does anyone know what the problem is?

Error: File Upload is currently unavailable.
DotNetNuke.Services.Exceptions.ModuleLoadException: Cannot access a closed file. ---> System.ObjectDisposedException: Cannot access a closed file. at System.IO.__Error.FileNotOpen() at System.IO.FileStream.Seek(Int64 offset, SeekOrigin origin) at System.Web.HttpRawUploadedContent.TempFile.GetBytes(Int32 offset, Int32 length, Byte[] buffer, Int32 bufferOffset) at System.Web.HttpRawUploadedContent.CopyBytes(Int32 offset, Byte[] buffer, Int32 bufferOffset, Int32 length) at System.Web.HttpInputStream.Read(Byte[] buffer, Int32 offset, Int32 count) at ICSharpCode.SharpZipLib.Zip.ZipInputStream.FillBuf(Int32 size) at ICSharpCode.SharpZipLib.Zip.ZipInputStream.GetNextEntry() at DotNetNuke.UI.Skins.SkinController.UploadSkin(String RootPath, String SkinRoot, String SkinName, Stream objInputStream) at DotNetNuke.Modules.Admin.FileSystem.WebUpload.cmdUpload_Click(Object sender, EventArgs e) --- End of inner exception stack trace ---