Nested IF statements

Due to serious lack of sleep I am having difficulties concentrating on the following:

The problem is this. The simple condiional statements work well on their own however, when the conditional statements are combined the code produces an error.

I am not concerned with the mathematical formulas.

For the curious though, the code simply generates a year-value. If no parameters are passed then it generates a random date between 1752 to the current year. If parameters are passed then it generates a random year-value between %1 and %2. If only one parameter is passed then a year-value is not generated.

CODE 1 (Works okay)
@echo off
if "%1"=="" set /a RndYear = %random% %% (%date:~6,4% - 1752 + 1) + 1752
if not "%1"=="" if "%2"=="" exit /b
if not "%1"=="" set /a RndYear = %random% %% (%2 - %1 + 1) + %1
exit /b %RndYear%
 
CODE 2 (Same code using nested IFs - does not work)
@echo off
if "%1"=="" (
   set /a RndYear = %random% %% (%date:~6,4% - 1752 + 1) + 1752
) else (
   if "%2"=="" (
      exit /b
   ) else (
      if not "%1"=="" set /a RndYear = %random% %% (%2 - %1 + 1) + %1
   )
)
exit /b %RndYear%

I have tried negating the conditions however, I receive the same error.

This may be a simple problem as it may be due to something I have overlooked. As I said, I'm dog-tired and mentally drained.

I have deliberately not included the error message because glancing at the code, both appear to be logically and lexically correct. My XP DOS version is 5.1.2600.