Well it's useful to have that error when the last parameter is missing to help catch coding problems. For your purposes you can use "" for the last parameter instead. This will actually insert "" into the INI file but surrounding quotes are ignored by $readini().

Code:
/writeini file.ini topic item $qt(value)

should work fine.

Use $+(",value,") instead of $qt(value) if you need to support mIRC versions older than 6.17.

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