While not exists Loop Throwing Error When I Have Else Condition at the End

I want to do a while loops that says while you don't see an error message, run this workflow. Else, if you do see the error message, take a screen shot of the entire screen.

When I add the else code in, the IDE throws a weird exception or error.

Here's the code in my script:

while not exists("ErrorScreenshot.png"):
           click(a)
           rightClick(a)
           #doubleClick(b)
           click(b)
           doubleClick(Pattern("1374609778702.png").similar(0.57))
           type(username)
           type(pwd)
           click("1374609885172.png")
           wait("1374609994953.png", 70)

           click("1374610198940.png")
           click("1374699689215.png")
           print username, pwd

      else:
           screen = Screen()
           file = screen.capture(screen.getBounds())
           print("Saved screen as "+file)

Here's the error message i get when I uncomment the else conditon:

[error] script [ *ModifyCredReadFromConfig ]] stopped with error at line --unknown--
[error] Could not evaluate error source nor reason. Analyze StackTrace!
[error] IndentationError: ('unindent does not match any outer indentation level', ('C:\\Users\\Sikuli\\AppData\\Local\\Temp\\sikuli-6590832730376844871.py', 40, 6, ' else:\n'))

Any ideas what is wrong? Is an else condition not allowed with while not exists?