You may or may not have come across this issue in a view. In some cases it is catastrophic, in other cases it is a simple change in the filter.

For example in this case, the issue is that one of the fields which is a workflow field and I tried to filter any items that were not "completed"

I went into the view design, then selected filters and set the filter for the field "onboard employee" to not equal "completed" thinking that it would work. The result was this message below.

So to fix this, you have to follow a simple procedure:

1. go into the list view, then on the "onboard employee" field, select the filter by value. in my case "completed" as per the picture below.

2. This will filter the items by this value, but interestingly it will put a FilterField1=Onboarde&FilterValue1=5 string in the URL. That is the value that you need (5).

This is an example of what you see in the url

http://portal07/SiteDirectory/Human%20Resources/onboarding/Lists/Employee%20List/AllItems.aspx?View={F2D76358-CF79-4D96-A619-7C0A7CE1598F}&FilterField1=Onboarde&FilterValue1=5

3. Go back to your view and then change the filter to not equal 5 instead of "completed"

This also applies to lookup values that are stored on other lists. for example if you have a look up field in a list and want to create a view based on an item in the master list then you need to follow this process (what you are trying to get is the ID of the underlying item in the master list, not the text).

Hope this helps someone.