2231295 - SUM error: Cannot find executable 'disp+work' in path: PATH

When you perform a Software Update Manager (SUM) upgrade, during the TOOLVERSXML_ROADMAP or SELECT_ROADMAP phase, you encounter errors similar to following:

1 ETQ399 Executing the command 'disp+work' for the 'non-ignorable' tool
'disp+work' in cur-path '(null)'
1 ETQ399 Output of 'disp+work' to be found in 'disp+work_cur.out'
1 ETQ399
1EETQ399 Error: Non-ignorable executable 'disp+work' in dir '<(><<)>current
tool path>' does not exist - missing!
1EETQ399 Last error code set is: Cannot find executable 'disp+work' in
path: PATH
Error: The command 'disp+work' from tool 'disp+work' could not be
executed successfully
1EETQ204 Upgrade phase "TOOLVERSXML_ROADMAP" aborted with severe errors
("<timestamp>")

Or:

1 ETQ201 Entering upgrade-phase "MOD_SELROADMAP/SELECT_ROADMAP"
("20131017150424")
4WETQ399 Cannot find 'tp' in current path!
4WETQ399 Cannot find 'R3trans' in current path!
4WETQ399 Cannot find 'R3load' in current path!
2 ETQ367 Connect variables are set for standard instance access
4 ETQ399 System-nr = '01', GwService = 'sapgw01' Client = '000'
4 ETQ399 Environment variables:
4 ETQ399   auth_shadow_upgrade=<null>
1 ETQ200 Executing actual phase 'MOD_SELROADMAP/SELECT_ROADMAP'.
1 ETQ399 Phase arguments:
2 ETQ399 Arg[0] = ''
1 ETQ399 SYSMANDEBUG_ASCSSYSNUM: ''.
1 ETQ399 SYSMANDEBUG_ASCSHOST: ''.
1EETQ399 Last error code set is 'Cannot find executable 'disp+work' in
path: PATH'
1EETQ204 Upgrade phase "SELECT_ROADMAP" aborted with severe errors
("<timestamp>")

SUM, upgrade, disp+work, executables, SELECT_ROADMAP, TOOLVERSXML_ROADMAP , KBA , BC-UPG-TLS-TLA , Upgrade tools for ABAP , Problem