Cygwin ash.exe rebaseall gives fork error

Somehow this week my cygwin installation broke down, giving the following error when I try to start it:

Error: Could not fork child process: Resource temporarily unavailable (-1).
DLL Rebasing may be required see 'rebaseall / rebase --help'.

So far so good, a google search easily points to many places explaining how to perform the rebasing. However, when I then follow the instructions to rebase:

1. Open cmd.exe as administrator
2. cd in \cygwin\bin
3. run ash /usr/bin/rebaseall

However, then I get a similar error to what I was trying to solve by rebaseing:

  0 [main] ash (14624) c:\cygwin\bin\ash.exe: *** fatal error - cygheap base mismatch 
detected - 0xCB8408/0xD28408.

This problem is probably due to using incompatible versions of the cygwin DLL.

Search for cygwin1.dll using the Windows Start->Find/Search facility
and delete all but the most recent version.  The most recent version *should*
reside in x:\cygwin\bin, where 'x' is the drive on which you have
installed the cygwin distribution.  Rebooting is also suggested if you
are unable to find another cygwin DLL.

  0 [main] ash 7140 fork: child -1 - forked process 14624 died unexpectedly, retry 0, 
exit code 0xC0000142, errno 11/usr/bin/rebase-trigger: 33: /usr/bin/rebase-trigger: 
Cannot fork

So, I searched for the cygwin1.dll build only one was found.

Does anyone have some clues what more I could try to fix this?

You need to delete the PortableGit folder

1. Go to the GitHub AppData folder: C:\Users\[username]\AppData\Local\GitHub
2. Delete the folder PortableGit*...