"Failed to execute deployed method 'ListOptions', column argument cannot be null" error

First of all I am a newcomer to Metastorm, and to the community, so apologies if this is a basic developer error.....

Secondly, I'm trying to prepopulate a drop down box in a form with name value pairs. Specifically to show empnames but the value being stored their empid so I can use this to populate other elements on the form. I've created a dataconnection to our Personnel database, created a data business object that uses that dataconnection, also a process business object with variables and now I've set about trying to populate that dropdown field bound to a specific business object variable.

When I use the 1 column list of values option everything works fine - when I choose either the empname or the empid from the data business object. When I use the name-value pairs option and choose the same in each one - either empname empname and empid empid - again it works fine. When I choose name value pair - Name and empid as value it comes up with the error above.

I noticed that when I populated with the 1 column list the dropdown it had a blank entry at the top so I changed the form - When user loads form event - to prepopulate the drop down with a specific name using assign variable activity. Again this works fine with either in the 1 column list option but not with a different name and different value in the pair. It also strangely works with empid as both name-value but not empname. I haven't as of yet tried the Code Activity activity to do the same.

I do notice however, when I did this with the 1 column list the blank entry still appeared only not at the top and I wonder if that's related.

I've tried changing the business object variable I''m binding to an integer as well as a text, and tried using a CAST statement in the SQL behind my data connection in case it is a type conflict but again with little joy - although I do not think this is the present issue..

I know this is very basic functionality, and I'm sure its possible, as we did something similar on our training course in the summer, but I'm now at a loss at how we did it / what to test next. Should I be using sql to populate the drop down ?

I am using Metastorm 9, and any suggestions at all would be welcome. Also apologies for the slightly convoluted first posting to the community.

John