Notice: Undefined index: custom-type

Hi
Could you check if your wpml-config.xml files in your theme or plugins are built correctly?

You have 2 <custom-types> opening tags and 2 closing tags </custom-types> . You should have just 1.

In the code below I removed them:

<wpml-config>
    <custom-fields>
        <custom-field action="copy">quantity</custom-field>
        <custom-field action="translate">custom-title</custom-field>
        <custom-field action="copy">weight</custom-field>
        <custom-field action="translate">custom-description</custom-field>
        <custom-field action="ignore">date-added</custom-field>
    </custom-fields>
    <custom-types>
        <custom-type translate="1">project</custom-type>
        <custom-type translate="1">service</custom-type>
        <custom-type translate="1">staff</custom-type>
        <custom-type translate="1">testimonial</custom-type>
        <custom-type translate="0">slide</custom-type>
        <custom-type translate="0">view</custom-type>
        <custom-type translate="0">gallery</custom-type>
        <custom-type translate="0">video</custom-type>
    </custom-types>
    <taxonomies>
        <taxonomy translate="1">prj-category</taxonomy>
        <taxonomy translate="0">media-tags</taxonomy>
    </taxonomies>
</wpml-config>

Could you test and let me know if it works?

Great! Which theme or plugin has provided this file?

Ok. Thanks to forward this topic to the Sailing theme author to fix this issue in its next version.