Modify parameter of an embedded chart in a protected worksheet

Hi Excel-friends,

I have a chart in a protected worksheet and I need to modify the scaleMin and ScaleMax property, very frequently. The chart is showing online data from an OPC server and is updated two times in a second. Thats why I cam not unprotect the sheet, do the action and protect it afterwards.

I am looking for a way, to modify the properties while the sheet and the chart are protected.

What I have:

Look inside my code:

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Xcel_Charts.xlsm

I get a runtime error (80004005), telling me that the method minimumScale has failed. In the moment I use Excel 2003 but later I want to run it in Excel2010.
If I remove the protection of the sheet, it is running well.

Excel Charts.JPG

Please help me.