In Bubble, this type of error occurs when trying to set something to oneself in a Conditional.
For example, when trying to change the unclickable setting and the text's value by using a button's Conditional.
In such cases, the issue may be resolved by referring to the source value in the Conditional's "when" rather than getting the value from oneself (in this case, Simpleprogressbar C).
I hope you can give it a try.