OS X Build button greyed out with x86 64-bit architecture

When I try to build an application for OS X, the Build button is greyed out when I select x86 64-bit as the Architecture.

What could cause this and what is the solution?

As a bit more background, I’m updating an app I developed in 2014 to make it compatible with Mac OS X Catalina’s 64-bit requirement. I have a current Xojo developer license for OS X, but am using Xojo 2016r1 as a short term fix because it offers the 64-bit Mac Build feature I need while still allowing the graphics code I used, which was later deprecated in Xojo 2018r3 (https://blog.xojo.com/2018/12/06/updating-code-that-used-the-graphics-property/).

Any advice/solutions is greatly appreciated.

I would use 2017r4 or 2018r1 or r2 instead
Secondly they build for an older version of the macOS SDK which may have its own set of issues when you get to Catalina

Thanks much, Norman. I’ll give that a try.

If you hover your mouse over the run or build button without clicking then it will tell you the error.