The error message "Could not modify stub dll (Error: failed to load runtime engine)" means that Dyalog APL is unable to find the file named dyalognnn[rt].dll (where nnn is a set of digits which will vary according to the Dyalog version). This file needs to be on the system path (names in the PATH environment variable).
Under Windows XP, you can check the definition of PATH and other environment variables by going to Control Panel, System, Advanced, Environment Variables.
Versions 12.1 and 12.0:
The directories that need to be in the PATH:
C:\Program Files\Dyalog\Dyalog APL nnn Unicode\bin\
and/or
C:\Program Files\Dyalog\Dyalog APL nnn Classic\bin\
nnn can be 12.1 or 12.0
Version 11.0:
nnn is 11.0
Version 10.1:
The installer should create an environment variable named DYALOGNETDIR101 and add %DYALOGNETDIR101%; to the path. Verify that DYALOGNETDIR101 points to the Dyalog "dotnet" folder and that %DYALOGNETDIR101% is listed in the PATH.
Further help:
Please use the diagnostic test function detailed here, and modify it for your particular circumstances. Copy the output from the function and paste it into an email to support@dyalog.com
r←dll_test121;LoadLibrary;GetLastError;GetEnvironmentVariable
r←⍬
'LoadLibrary'⎕NA'u kernel32|LoadLibrary* <0T'
⎕NA'u kernel32|GetLastError'
'GetEnvironmentVariable'⎕NA'u kernel32|GetEnvironmentVariable* <0T >0T U'
r,←LoadLibrary⊂'dyalog121rt_unicode.dll'
r,←GetLastError
r,←LoadLibrary⊂'C:\Program Files\Dyalog\Dyalog APL 12.1 Unicode\bin\dyalog121rt_unicode.dll'
r,←GetLastError
r,←GetEnvironmentVariable'PATH' 4096 4096