This isn't preventing anything from compiling or working right. The line does format as currency. But when I hover over where it says the error is, it says "} expected". There's nothing wrong here, just a XAML bug I'm assuming.
And check out the errors. Why do they show as errors, yet the project builds and runs just fine? And the line in question is actually line 79, not 78 like the error reports.
Not a big deal, I just hate seeing any squiggly lines in my code when there's nothing wrong, and errors that aren't errors.