# \[fmx pro\] Left side of assignment operator must be variable error problem

**URL:** <https://forum.kirupa.com/t/fmx-pro-left-side-of-assignment-operator-must-be-variable-error-problem/139159>\
**Category:** Uncategorized\
**Created:** [March 1, 2005, 1:18am UTC](https://forum.kirupa.com/t/fmx-pro-left-side-of-assignment-operator-must-be-variable-error-problem/139159 "2005-03-01T01:18:22Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![mrbill](https://avatars.discourse-cdn.com/v4/letter/m/8dc957/32.png) [@mrbill](https://forum.kirupa.com/u/mrbill)\
**Post date:** [March 1, 2005, 1:18am UTC](https://forum.kirupa.com/t/fmx-pro-left-side-of-assignment-operator-must-be-variable-error-problem/139159/1 "2005-03-01T01:18:22Z")

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I’m somewhat new and trying to learn actionscript. I’m getting and error that has me puzzled.

**Error** Scene=Scene 1, layer=actions, frame=1:Line 2: Left side of assignment operator must be variable or property.  
bg-mb\_mc.\_alpha=50;

I have a timeline with 3 jpgs on it that have been converted into symbols.

bg-gooto\_mc is an instance of bg-gooto  
bg-mb\_mc is an instance of bg-mb  
bg-lace\_mc is an instance of bg-lace

When I try … bg-mb\_mc.\_alpha=50; I get the error.  
using setproperty ("\_level0.bg-mb\_mc", \_alpha, 45); works ok.

It would be greatly appreciated if someone would please explain the problem.