Hi MT2-ss welcome to Subsim help is at hand you have a PM from me with link to my SH3 download already patched to 1.4 just follow instructions and you'll be up and running in short order Sir.
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The Pride Runs Deep We Look After Our Own
Your SH3 maybe already patched to 1.4 and trying to add the 1.4 patch to a SH3 install thats already patched that maybe why your getting that error message also i would'nt install SH3 in program/files x86 it will mess up your campaign saves due to windows security thinking SH3 is a virus reading and writing to your SH3 career save folder in your documents.
heres a screenie of my SH3 sh3 exe already patched to 1.4 to check yours just move your mouse over the SH3.exe if same as the one in the picture below your good to go Sir.
If you need any further help add to this post or drop me a line.