In the Properties dialog of the control, select the General Tab and then select the Allow Multiple Selections checkbox.

Have you tried using different names to see if there is a problem with that particular name? 

Hope this helps.

Steve

In the properties>general it just says Max lines and the value is set to 4

What version of InfoPath are you using? I was referring to the 2010 version. If you are using 2007, then I'll need to find a copy of that somewhere to check this.

Found one. Actually, InfoPath 2007 doesn't appear to have a People/Group Picker control. Hmm...

Are you sure that you don't have two sections under the General tab? I show "SharePoint List Properties" and "Appearance". The "Allow multiple selections" checkbox is the first field.

The default behaviour for InfoPath people picker (2007) is it'll allow you to select multiple people.  So when you say its an error in the apps logs what apps logs are you referring to?  Is it the logs when the worklow executes or are you referring to an error in the K2?

I can actually add more poeple to the people picker. The error I get in the Windows App log is that it wants to remove the semi-colon between the entries so it merges them into one string causing the cannot find the user error.

I've never seen that and I used the contact selector a lot in InfoPath. 

You may want to review the following post to make sure its not a configuration issue with setting up the control in InfoPath 2007:  http://stevenboldt.com/blog/post/2009/09/22/InfoPath-Form-Contact-Selector-Control-Doe28099s-and-Done28099ts.aspx

If that doesn't help try recreating the problem on a brand new infopath form only adding the contact selector and if you get the same error maybe post that form and we can take a look.