Issue Creating Atlas

[justinISO]

NGUI Version 3.11.1
Unity 5.5.0f3

Something I have done a million times before has started throwing errors for me. I have selected sprites in the project view and clicked create atlas in the atlas maker and instead of creating an atlas I now get these errors.

Unsupported texture format - needs to be ARGB32, RGBA32, RGB24, Alpha8 or one of float formats
UnityEngine.Texture2D:EncodeToPNG()
UIAtlasMaker:UpdateTexture(UIAtlas, List`1) (at Assets/NGUI/Scripts/Editor/UIAtlasMaker.cs:601)
UIAtlasMaker:UpdateAtlas(UIAtlas, List`1) (at Assets/NGUI/Scripts/Editor/UIAtlasMaker.cs:714)
UIAtlasMaker:UpdateAtlas(List`1, Boolean) (at Assets/NGUI/Scripts/Editor/UIAtlasMaker.cs:697)
UIAtlasMaker:OnGUI() (at Assets/NGUI/Scripts/Editor/UIAtlasMaker.cs:1061)
UnityEditor.DockArea:OnGUI()

NullReferenceException: Object reference not set to an instance of an object
System.IO.File.WriteAllBytes (System.String path, System.Byte[] bytes) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.IO/File.cs:595)
UIAtlasMaker.UpdateTexture (.UIAtlas atlas, System.Collections.Generic.List`1 sprites) (at Assets/NGUI/Scripts/Editor/UIAtlasMaker.cs:602)
UIAtlasMaker.UpdateAtlas (.UIAtlas atlas, System.Collections.Generic.List`1 sprites) (at Assets/NGUI/Scripts/Editor/UIAtlasMaker.cs:714)
UIAtlasMaker.UpdateAtlas (System.Collections.Generic.List`1 textures, Boolean keepSprites) (at Assets/NGUI/Scripts/Editor/UIAtlasMaker.cs:697)
UIAtlasMaker.OnGUI () (at Assets/NGUI/Scripts/Editor/UIAtlasMaker.cs:1061)
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)

Anyone else having this issue?

[ArenMook]

Select the texture and check its import type. Make sure it's set to truecolor and that it doesn't get compressed. Your platform may be forcing a certain format that can't be overwritten via code.