Andy,
The exception appears to be coming from DotNetNuke.Services.Localization.Localization.LocalizeControlTitle()?
That method in the core looks at the Title you put for the module when adding it to the page. If that is empty, it attempts to get it from the module control's resx file with key "ControlTitle"_[controlKey (toLower)].Text. I think it needs a control title for Search Results and other things.
First re-check the path of your resx file. If that's good, then see what the control key is set for the module control. For simplicity, I like to make the control key the same as the control file name. So if my control is named "EnterInfo.ascx", I would make the key "enterinfo". Go to Host > Extensions, edit the module, select the module definition, edit the controls and make sure the key is "enterinfo". Hopefully that will get rid of this error.