VBS advanced expression to check for white space

Summary:

We need to rebuild an AC rule that checked a field for any spaces in it- if spaces found then error to ensure user removes any spaces in the field (it is a free text field). I have tried this in VBS but it is not triggering.

Content (please ensure you mask any confidential information):

We have created this Validation rule on Change Assignment:

But it isn't working - have I got something wrong on the Reg Exp for spaces? Tried a few variations from searching online but nothing seems to work.

I have done similar validation rules for other data formatting checks (like numeric characters only etc) which are working fine - but this one for checking Spaces is not happy!