Index: wp-admin/includes/post.php
===================================================================
--- wp-admin/includes/post.php	(revision 21151)
+++ wp-admin/includes/post.php	(working copy)
@@ -62,7 +62,7 @@
 			} else {
 				return new WP_Error( 'edit_others_posts', $update ?
 					__( 'You are not allowed to edit posts as this user.' ) :
-					__( 'You are not allowed to post as this user.' )
+					__( 'You are not allowed to create posts as this user.' )
 				);
 			}
 		}
Index: wp-includes/class-wp-xmlrpc-server.php
===================================================================
--- wp-includes/class-wp-xmlrpc-server.php	(revision 21151)
+++ wp-includes/class-wp-xmlrpc-server.php	(working copy)
@@ -3726,18 +3726,18 @@
 		$post_author = $user->ID;
 
 		// If an author id was provided then use it instead.
-		if ( isset($content_struct['wp_author_id']) && ($user->ID != $content_struct['wp_author_id']) ) {
+		if ( isset( $content_struct['wp_author_id'] ) && ( $user->ID != $content_struct['wp_author_id'] ) ) {
 			switch ( $post_type ) {
 				case "post":
-					if ( !current_user_can('edit_others_posts') )
-						return(new IXR_Error(401, __('You are not allowed to post as this user')));
+					if ( !current_user_can( 'edit_others_posts' ) )
+						return( new IXR_Error( 401, __( 'You are not allowed to create posts as this user.' ) ) );
 					break;
 				case "page":
-					if ( !current_user_can('edit_others_pages') )
-						return(new IXR_Error(401, __('You are not allowed to create pages as this user')));
+					if ( !current_user_can( 'edit_others_pages' ) )
+						return( new IXR_Error( 401, __( 'You are not allowed to create pages as this user.' ) ) );
 					break;
 				default:
-					return(new IXR_Error(401, __('Invalid post type')));
+					return( new IXR_Error( 401, __( 'Invalid post type' ) ) );
 					break;
 			}
 			$author = get_userdata( $content_struct['wp_author_id'] );