Don't use SystemException but a PropertyListException to indicate something went wrong.

plist-cil/NSObject.cs

@@ -373,7 +373,7 @@ namespace Claunia.PropertyList
             }
             catch (IOException)
             {
-                throw new SystemException("The given object of class " + o.GetType() + " could not be serialized and stored in a NSData object.");
+                throw new PropertyListException("The given object of class " + o.GetType() + " could not be serialized and stored in a NSData object.");
             }
         }
 

plist-cil/NSString.cs

@@ -163,7 +163,7 @@ namespace Claunia.PropertyList
                 }
                 catch (Exception ex)
                 {
-                    throw new SystemException("Could not encode the NSString into UTF-8: " + ex.Message);
+                    throw new PropertyListException("Could not encode the NSString into UTF-8: " + ex.Message);
                 }
             }
 

plist-cil/PropertyListException.cs

@@ -0,0 +1,77 @@
+// plist-cil - An open source library to parse and generate property lists for .NET
+// Copyright (C) 2015 Natalia Portillo
+// Copyright (C) 2016 Quamotion
+//
+// This code is based on:
+// plist - An open source library to parse and generate property lists
+// Copyright (C) 2014 Daniel Dreibrodt
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+using System;
+using System.Runtime.Serialization;
+
+namespace Claunia.PropertyList
+{
+    /// <summary>
+    /// The exception that is thrown when an property list file could not be processed correctly.
+    /// </summary>
+    [Serializable]
+    public class PropertyListException : Exception
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="PropertyListException"/> class.
+        /// </summary>
+        public PropertyListException()
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="PropertyListException"/> class.
+        /// </summary>
+        /// <param name="message">
+        /// The error message that explains the reason for the exception.
+        /// </param>
+        public PropertyListException(string message) 
+            : base(message)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="PropertyListException"/> class.
+        /// </summary>
+        /// <param name="message">
+        /// The error message that explains the reason for the exception.
+        /// </param>
+        /// <param name="inner">
+        /// The exception that is the cause of the current exception, or <see langword="null"/>
+        /// if no inner exception is specified.
+        /// </param>
+        public PropertyListException(string message, Exception inner) 
+            : base(message, inner)
+        {
+        }
+
+#if !NETCORE
+        protected PropertyListException(SerializationInfo info, StreamingContext context) 
+            : base(info, context)
+        {
+        }
+#endif
+    }
+}

plist-cil/PropertyListFormatException.cs

@@ -32,7 +32,7 @@ namespace Claunia.PropertyList
     /// </summary>
     /// @author Daniel Dreibrodt
     /// @author Natalia Portillo
-    public class PropertyListFormatException : Exception
+    public class PropertyListFormatException : PropertyListException
     {
         /// <summary>
         /// Creates a new exception with the given message.