scrollbar:visible:true doesn't exist you need to use the ScrollPane attribute showScrollBar="true". Take a look at the Widget Reference page.
Else, ScrollPane, because of its unconsistant content doesn't have any content size. In this case, it doesn't make sens to put a ScrollPane in an inlineLayout.
ScrollPane need to be placed in widget with auto spaced layout like GridLayout, BorderLayout (only on center). Else you can specify manualy the min size of your ScrollPane widget with the min-size style property
By default the screen layout is GridLayout(1,1) which is compatible with ScrollPane, and ScrollPane scrollBar is visible why not simply use this syntax ?
<screen>
<scrollpane>
<!-- here your screen content -->
</scrollpane>
</screen>