What does "error: expected expression before '/' token" really mean?

 Can someone tell me please what this error really means?:

"error: expected expression before '/' token"

Googling says it is from using C++ style comments, in C code, which is
not the case here.

I can find no place where there actually *is* a '/' token in relation
to the error:

avr-gcc (AVR_8_bit_GNU_Toolchain_3.4.4_1229) 4.8.1

 [GCC]     : Compiling C File: "Version/version.c" to
"[../Firmware_Project/Project/Object/]
../Firmware_Project/Project/Object/Version/version.o"

J:\APPS/AVR_TC_344_1229/bin/avr-gcc [see command line below]
<command-line>:0:11: error: expected expression before '/' token

Version/version.c:25:48: note: in expansion of macro 'MODEL_STR'
 const char Model_Prj_str[]      VERSION_INFO = MODEL_STR;
/* Model */
                                                ^
This is how MODEL_STR has been defined for a very long time (changed
the project name for posting here):

-DMODEL_STR=\"Project\"

This has something to do with the build system and not the actual
source code, as the build system is what was recently changed.
The error goes away if I take the multiplication out of this line:

CDEFS += -DALARM_SET_POINT_MAX=(15U*60U)

so it just reads as :

CDEFS += -DALARM_SET_POINT_MAX=15

That definition is not used, nor even included in anyway outside of
the command line, in the file that is complaining about the '/' token.

I can invoke the same error by adding parentheses around this line:

CDEFS += -DSCRN_Y_BYTES=$(SCRN_HEIGHT)/8U

to yield:

CDEFS += -DSCRN_Y_BYTES=($(SCRN_HEIGHT)/8U)

This is the compile command line, split on spaces due to its length to show it
here, normally it would be one LONG line:
J:\APPS/AVR_TC_344_1229/bin/avr-gcc
-c
-mmcu=atxmega128a1
-DSCRN_HEIGHT=32U
-DSCRN_LENGTH=120U
-DSCRN_LEFT=0U
-DSCRN_TOP=0U
-DSCRN_RIGHT=120U-1U
-DSCRN_BOTTOM=32U-1U
-DSCRN_X_BYTES=120U
-DSCRN_Y_BYTES=32U/8U
-DMODEL_NAME_TEXT=\"CompanyName\"
-DLOGO_MODEL_NAME=\"Name\"
-DLOGO_WIDTH=120U
-DLOGO_HIGHT=21U
-DLOGO_TEXT_POSITION_X=SCRN_LEFT+1U
-DLOGO_TEXT_POSITION_Y=SCRN_TOP+20U
-DLOGO_TEXT_FONT_SIZE=FONT_DINA_SIX_DOT
-DPCB_REV_A=1U
-DALARM_SET_POINT_MAX=15*1
-DMODEL_STR=\"Project\"
-DFIRMWARE_NUMBER=0U
-DFIRMWARE_REV_STR=\"v0.0.0\"
-DFIRMWARE_REV_NUMBER_STR=\"000\"
-DBACKLIGHT_BUTTON_TIME=10U
[Many other -D's snipped]
-IVersion/
[Many other -I's snipped]
-I.
-g
-Os
-funsigned-char
-funsigned-bitfields
-std=gnu99
-Wa,-adhlns=../Firmware_Project/Project/Object/Version/version.lst
-DF_CPU=4000000UL
-Datxmega128a1
-DNEW_BUILDNUMBER=911
-DNEW_BUILDNUMBER_TEXT=\"911\"
-MMD
-MP
-MF ../Firmware_Project/Project/Dep/version.o.d
Version/version.c
-o ../Firmware_Project/Project/Object/Version/version.o