Reference variables turn (x) format for negative numbers into text

Summary

Reference variables turn (x) format for negative numbers into text, so SUM(A:Z) doesn't work

Content

We load a cell into a reference variable then use this to populate another sheet, a series of values, some reference variables are then summed,  (x) format for negative numbers appear to be turned into text so the SUM fails, despite the source being able to be totalled correctly

This means that SUM(A:Z) doesn't work, however strangely A+B+C...+Z does work

Is there anyway to alter the data type of the reference variable to cater for the (x) format