system() expects a string (or a list of strings) — not a mixture of whitespace-separated strings and barewords.

system('"C:\\Program files\\Borland\\SilkTest\\partner.exe" -q -r "C:\
+\Perfrom_Acce\\Investigate\\Investigate_ACCEPTANCE.t" WelcomePagesOn'
+);
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(note the single quotes around the entire command)