The style item key of the symbol in the style contains unsupported characters and cannot be shared. Style item key cannot contain any special characters ( / \ : * ? < > | ).
The <value> parameter refers to the symbol name.
Right-click the analyzer message and click Open Style in Catalog View. Select the symbol item, and in the Details panel, click Description. If the Details panel is not open, on the View tab, in the Options group, click Details Panel . Remove any invalid characters from the Key field and click Apply.
For more information, see Share a web style and Analyze your GIS resource.