Limiting the value of t should solve the problem:

t = Math.min(time - key(n).time,10);

Dan

From: "D" <dow.hanson@gmail.com>
To: "After Effects Mail List" <AE-List@media-motion.tv>
Sent: Wednesday, September 25, 2013 8:38:51 AM
Subject: Re: [AE] Inertial bounce expression keeps being disabled randomly...

Line 12, same line as the other version of the expression (which was line 10).

On 25 September 2013 16:34, Lloyd Alvarez <lists@aescripts.com> wrote:

What line number are you getting the error on?

On Wed, Sep 25, 2013 at 11:30 AM, D <dow.hanson@gmail.com> wrote:

Looks good. I'll try and persuade these guys to buy that script. Also, I've just had more expression failures but still get the divide by zero error when I try to paste your solution above. Is this a bug beyond the expression?

On 25 September 2013 15:40, Lloyd Alvarez <lists@aescripts.com> wrote:

You can use this to batch update all the expressions in your project: http://aescripts.com/pt_expressedit/

On Wed, Sep 25, 2013 at 9:46 AM, D <dow.hanson@gmail.com> wrote:

Yes, was guessing that. Too many instances to replace with an upcoming deadline though so quick fixing with the aid of your script for now.

On 25 September 2013 14:35, Lloyd Alvarez <lists@aescripts.com> wrote:

The expression will keep failing unless you account for that divide by zero error.

On Wed, Sep 25, 2013 at 9:23 AM, D <dow.hanson@gmail.com> wrote:

Thanks Lloyd. Funnily enough, I just found your script 'Activate Disabled Expressions'. I purged all memory then applied the script. Emptying the memory seems to allow them back on. Great script. Next time I get a mass disablement I'll try your solution.

On 25 September 2013 12:35, Lloyd Alvarez <lists@aescripts.com> wrote:
As the error suggests, it gets disabled because it tries to divide by zero.. Most probably because you are in negative time due to this: t = time - key(n).time;

You can protect against that in several ways but here's a quick cheeky way:

amp = .1;
freq = 2.0;
decay = 12.0;
n = 0;
if (numKeys > 0){ n = nearestKey(time).index;
if (key(n).time > time){ n--;
}} if (n == 0){ t = 0;
}else{ t = time - key(n).time;
} if (n > 0){ v = velocityAtTime(key(n).time - thisComp.frameDuration/10);
d= Math.exp(decay*t);
if ( d == 0 ) d= 0.0001;
value + v*amp*Math.sin(freq*t*2*Math.PI)/d;
}else{value}

Cheers,
Lloyd

On Wednesday, September 25, 2013, D wrote:

...confusingly, the expression will sometimes continue to work on other layers in the same comp on both position and scale parameters whilst some get disabled.

On 25 September 2013 10:40, D <dow.hanson@gmail.com> wrote:

Hi

The expression I'm using looks like this:

amp = .1;

freq = 2.0;

decay = 12.0;

n = 0;

if (numKeys > 0){ n = nearestKey(time).index;

if (key(n).time > time){ n--;

}} if (n == 0){ t = 0;

}else{ t = time - key(n).time;

} if (n > 0){ v = velocityAtTime(key(n).time - thisComp.frameDuration/10);

value + v*amp*Math.sin(freq*t*2*Math.PI)/Math.exp(decay*t);

}else{value}

It works most of the time then will randomly get disabled across lots of layers and will not allow me to re-enable until I've restarted AE (v5.5). This is the error:

--

After Effects warning: invalid numeric result (divide by zero?)
Expression disabled.

Error occurred at line 10.
Comp: 'XXX'
Layer 17 ('XXX')
Property: 'Scale'

--

I have no real knowledge of how expression code works. I cut and paste when I use them. The project is 4 minutes long and the expression occurs across many comps and typically as the deadline approaches the error is now cropping up often. Any help appreciated.

Thanks.