CFX initialization error with sandbox security enabled

I've found that CFX_HTTP5 works fine with CF10 if I have sandbox security turned off.  However when I turn the sandbox on, the CFM page containing the CFX_HTTP5 tag will return a blank page and generate an error in the application.log "Could not initialize class coldfusion.tagext.NativeCfx"

The top of the stack trace looks like this:

Could not initialize class coldfusion.tagext.NativeCfx The specific sequence of files included or processed is: D:\Staging\cfxtest.cfm, line: 13 "

java.lang.NoClassDefFoundError: Could not initialize class coldfusion.tagext.NativeCfx

    at coldfusion.tagext.CfxTag.doStartTag(CfxTag.java:108)

    at coldfusion.runtime.CfJspPage._emptyTcfTag(CfJspPage.java:2795)

The cfxhttp5.dll is in C:/ColdFusion10/cfusion/CustomTags folder

I have fiddled with read, read+execute permissions and sandbox file paths such as:

c:\coldfusion10\cfusion\lib and lib\-

C:/ColdFusion10/cfusion/CustomTags/ and /-

C:/ColdFusion10/cfusion/lib/CFXNeo.dll

Platform is CF10 Enterprise 64-bit w/HF16 on Windows 2012.  Java 1.8.0_45