Unterminated format specifier exception keeps occuring and I don't know why.

[Enjoys Math via Digitalmars-d-learn]

This weird exception keeps occuring and visual D is not bringing 
me to the place in my code that might be calling it.

Message:

First-chance exception: std.format.FormatException Unterminated 
format specifier: "%" at 
C:\D\dmd2\windows\bin\..\..\src\phobos\std\format.d(830)


I've gotten rid of it before, but I'm not sure how.

Here's the call stack:
        KernelBase.dll!76e1d8a8 
 	___LIGHTSHOWAPP.exe!_D2rt9deh_win329throwImplFC6ObjectZv() + 
0x2a bytes	D
        
___LIGHTSHOWAPP.exe!std.exception.enforceEx!(std.format.FormatException).enforceEx!bool.enforceEx(
 uint line ) Line 618 D
 
	___LIGHTSHOWAPP.exe!std.format.FormatSpec!char.FormatSpec.writeUpToNextSpec!(std.array.Appender!(char[])).writeUpToNextSpec( std.format.FormatSpec!char.FormatSpec* this ) Line 831	D
 
	___LIGHTSHOWAPP.exe!std.format.FormatSpec!char.FormatSpec.__unittestL848_2148.__dgliteral1( void* this ) Line 878 + 0x20 bytes	D
 
	___LIGHTSHOWAPP.exe!std.exception.assertThrown!(std.format.FormatException, bool).assertThrown( uint line ) Line 231 + 0xb bytes	D
 
	___LIGHTSHOWAPP.exe!std.format.FormatSpec!char.FormatSpec.__unittestL848_2148() Line 879	D
 	___LIGHTSHOWAPP.exe!_D15bounded_2d_geom9__modtestFZv() + 0x8 
bytes	D
 
	___LIGHTSHOWAPP.exe!_D4core7runtime18runModuleUnitTestsUZ14__foreachbody1MFPS6object10ModuleInfoZi() + 0x45 bytes	D
 
	___LIGHTSHOWAPP.exe!_D6object10ModuleInfo7opApplyFMDFPS6object10ModuleInfoZiZ9__lambda2MFyPS6object10ModuleInfoZi() + 0xf bytes	D