On Monday, August 26, 2013 4:23:21 PM UTC-4, Michael Marshall wrote:
My investment has an initial cash outflow of $1000 followed by series of losses on this investment thus all remaining cash flows are negative. I was interested in knowing my loss in terms of internal rate of return for this investment so I tried using Excel IRR function with my data listed below but I was given a #NUM! error in Excel 2010 using the IRR function. My cash flows are as follows -1000 -644.89 -338.33 -87.34 I did try an alternative IRR function that is part of tadXL Excel add-in which is no longer available online and it reported a correct IRR for this investment. So what makes tadXL report an IRR for all negative cash flows and Excel IRR function is unable to find the internal rate of investment where investment makes no money and there are all losses.

If you are wondering how did I come about the cash flows I posted in my original post in the first place

Then I must say that the cash flows I listed earlier as

-1000
-644.89
-338.33
-87.34

weren't the ones I had in the first place.

These cash flows were the left overs of the original cash flows for which I desired to find the complete IRR solution set

And here were the original cash flows listed below where I had an investment of $1000 as cash outflow followed by four cash inflows of $500, $400, $300 and $100

-1000
500
400
300
100

The first IRR solution turns out to be 14.49% ( you can confirm this using Excel IRR function as follows )

=IRR( {-1000, 500, 400, 300, 100} )

Once the first IRR solution was found, I got left with the following cash flows which I had listed in the opening of my message

-1000
-644.89
-338.33
-87.34

For these cash flows Excel IRR returned #NUM! errror and I had to resort to using tadIRR function to find the second IRR which turns out to be -136.92%

Once the second IRR solution was found using tadIRR, I was left over with the following cash flows

-1000
-275.66
-236.55

And anyone who has little knowledge of algebra would know how to solve for the remaining two IRR values using a formula that results in the following two remaining IRR values

-113.78 + 46.64i %
-113.78 - 46.64i %

In conclusion, using my method and tadXL software I was able to find the complete IRR solution to the following cash flows

-1000
500
400
300
100

as

IRR = { 14.49%, -136.92%, -113.78 + 46.64i %, -113.78 - 46.64i % }

So @JoeU

Do you still question my authority on the subject matter for which I call myself a FinancialEngineer ?