Plugin not working

I'm trying to add a plugin and it isn't doing anything. When we add the plugin to the feed xml is it case sensitive or requires lower case?

public class FeedManagerPlugin
    {
        public virtual string ReadAttributeValue(Product product, ProductAttributeCombination productAttributeCombination, string feedColumName, string typeFeed)
        {
            if (product.Sku.StartsWith("WN-") || product.Sku.StartsWith("WU-") || product.Sku.StartsWith("WR-") || product.Sku.StartsWith("WI-"))
                return product.Sku.Substring(3);
            else
                return product.Sku;
        }
    }

You can use any case characters.

So why would it not pick it up?

Here's the snippet from the XML file:

<FeedAttribute>
    <Id>15</Id>
    <FeedCaption>Manufacturer Part Number (MPN)</FeedCaption>
    <FeedName>mpn</FeedName>
    <FieldNameCode>plugin:ReplaceWs</FieldNameCode>
    <ConvertValues />
    <CharsLimit>70</CharsLimit>
    <Required>false</Required>
    <IgnoreNullOrEmpty>false</IgnoreNullOrEmpty>
    <UseCDATA>false</UseCDATA>
    <ActionId>0</ActionId>
    <AdvancedField>false</AdvancedField>
    <RowSourceType>0</RowSourceType>
    <AttributeControlType>0</AttributeControlType>
  </FeedAttribute>

Did you add this file ReplaceWs.DLL to the  plugin folder (FoxnetSoft.FeedManager)?

Yes, created a plugins folder under FoxnetSoft.FeedManager and put that file in that folder.

Does it go in the root folder?

>Does it go in the root folder?
Copy this DLL file to the root plugin folder.

Yeah, that's still not working. Any other suggestions?

I am sorry for my mistake.

Copy plugin to this folder
~/Plugins/FoxNetSoft.FeedManager/Plugins/

Example of path
/Plugins/FoxNetSoft.FeedManager/Plugins/yourpluginname.dll

Restart nopcommerce after it.