Adding daily run hours to cumulative total hours

I have a spread sheet that among other things gives me a total of equipment running hours ie. H30 =sum(H36+K36) H36 is the previous total now approx 12531:30 hrs, the running hours daily, up to 24 hrs (K36) are added to this total, the relevant locations are formatted Custom [hh:mm] a new page is created each day using a macro.
recently when the page was updated I had a #data error in the total cell (H30) this is now persistent and I can't seem to get rid of it.
I think it might be because of the high number count of hrs, if I reduce the total hours in the cell the error goes away.
Is there a maximum number that the cells can handle ??

I have tried that format and still get the same #DATA error.
If i reduce the cumulative hours in cell H36 eg. from 12531:30 to 2531:30 the error goes away ?????? I'm using Excel 2010 btw, i was wondering if my installed Excel is corrupt as this error has started popping up in other cells but again only when the cells reach higher numbers usually above 10000:00.

Yes there is a macro involved
The macro creates a new day (work sheet) assigns the date etc and carries over the hours etc from the previous sheet and populates the new day sheet, then the formula adds yesterdays hours (cumulative) to today's hours on this new sheet, this is when the error occurs.

Try opening a new worksheet, format used cells [HH]:mm, input 9999:33 in A1, enter 24:00 in A2 make A3 = a1+A2 ok
now input 99999:22 into A1 it comes up with a Data error
If you enter 999999:22 into A1 it is ok weird!!!!

Anyone else with ideas. I have the same problem in my worksheets.
As long as A1 or A2 stay below 9999:00 the formula works okay.
I have tried text and custom formats but the problem stays.

Rodstew does a good job of describing the problem

Have a read here:

http://support.microsoft.com/kb/214386