When attempting to load Lowrance (.usr) files as GPS assets, I receive the error listed below.
(The same error is generated wether the files are stored in V2.0 or V3.0)
Thanks for your help.

(error msg)
Non-negative number required.
Parameter name: capacity


at System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument argument, ExceptionResource resource)
at System.Collections.Generic.List`1..ctor(Int32 capacity)
at #=qxetnXaAP$OIpMEra0B6NOgrUfbH0PCCw50MCDr5oNVKBvil5r34n1dU32OTGRDEFqXcGiLY09sZIeqh5PPFY5A==.#=qJBEqVmFS34gb4uSE1lenwA==(BinaryReader #=qi2cK_ICXbVbRk1twt$0$qw==, Int32 #=qdkGd7leivaKgpAZtChDM9Q==, DateTimeOffset #=qNWCdn_2$BWsfe4a9gRgSoA==)
at #=qxetnXaAP$OIpMEra0B6NOgrUfbH0PCCw50MCDr5oNVKBvil5r34n1dU32OTGRDEFqXcGiLY09sZIeqh5PPFY5A==.#=qKPGzLg8INHKCfh2zd_GadLLAAfFfae7pGL6NAv6aZZc=(String #=qpf$xb6ZeirssOiKiJ9IdkA==, String #=qw9RDBAbeyiZ436O4qNpx2g==, GPSSounderProfile #=q5$priJlzPpi8JqebIuHB6Q==)
at #=qE00p$cVnk2C6KLykG$PhFHY$GjvSETXJXYUic5ezVs9FFyPpW29$NyIMBcW7T$Lw_SNZm4dacj19bhP4GtFDLw==.#=q6vOd27CVZaL18EMxaEyDPqpQLBB3mdXjkjU6249jztE=(Object #=qlGwY3HMtlGTbXaa9z8HXMA==, DoWorkEventArgs #=qUFUVxxfy9DWAWkyF0PZo9A==)

Solved.

The externally created waypoints saved to my Lowrance were either incorrectly nammed or not at all. All waypointss on the device, including those associated with routes, get dumped to the MSD card when saving for export.

Remedy;
I deleted any routes, trails, and waypoints that were unecessary or created externally. The waypoints now load correctly.