[SalesForce] Restrict picklist values based on custom lookup field’s value

PICKVALS have a number of limitations that are often very difficult to work with.

In my experience, a rule that refers to a single value picklist can only refer to the current and previous value PRIORVAL of the picklist in a (valuefield, "textvalue") format. If it's a multi-select picklist, then you can use ISPICVAL(CONTAINS(valuefield, "textvalue1", textvalue2,...) or similar syntax (sorry, but I didn't have time to verify this is the correct way to order this before posting).

If you want the "Does not contain" or Boolean negative", you can use NOT(PICKVAL(valuefield, "textvalue") as an argument in your expression. What I've observed is that if you want if new value AND old value conditions type of validation rule, it's often best to set it up like: AND(ISPICKVAL(valuefield,"textvalue"), PRIORVAL("textvalue")). The editor will expect PRIORVAL to have an ISPICKVAL in front of it, but will only want one ISPICKVAL in the expression if there's two PICKVALS contained in the expression. The help on this is rather vague other than to tell you there are limitations on what you can do with PICKVALS.

Sometimes, it's nearly impossible to create a single validation rule for PICKVALS that address what you're trying to accomplish because they have so many limitations in SF. It can be very trying on one's patience and time-consuming. The syntax is quite different to what we're used to working with in APEX and other languages, or so it seems to me.

Notice that you have two Technologies columns. The first one, which is of type apex:inputField works. I do not believe apex:outputField supports the action you want because the fields are read-only. If you want the user to be able to select new values, you need to use the former. It looks like inputField works as desired without custom code, removing your need for a controller as well. If you need further assistance with how to manipulate apex:SelectList components, I recommend asking a more directed question to that effect.

From a best practice standpoint, you should have your column headers reference the $ObjectType global, for example:

<apex:column headerValue="{!$ObjectType.Contact.Fields.Level__c.Label}">