So... you have the following code:
propertyPageObj.FindChildByXPath(suiteVariableObj.txtboxStreetNum).Keys("661")
So... the question is... what does your code do if it is unable to find the child object?
See, if it can't find the object, then propertyPageObj.FindChildByXPath(suiteVariableObj.txtboxStreetNum) returns a null object... basically, nothing... so, it can't execute the Keys function... because there is no Keys function on the null object.
Better coding practice is to first check to see if you find the object before you try any processes against it.
My guess is that the XPath is different on IE11 than it is on Chrome... hence why it's working on Chrome. So... if the XPath is different, the function will return null, and your code will error out.
Double check the XPath in the IE environment. I'm betting it's different... in which case, you're going to need to go a little fancier with your suiteVariableObj.txtboxStreeNum and actually make it "smart" to detect the browser type and return a different XPath.