Problem with dynamic chart

I am trying to create a dynamic chart that pulls calculations from a second file to display the last 13 months of data logged. I am having a problem with my formula-for example, the formula is reading the cells containing "=A13", and trying to put this value in the chart. I only want the formula to read the cell information when it contains a the actual information pulled from the second file.

This is how I have it set up so far:

Named Ranges:
chtcats=OFFSET(Data!$A$2,COUNTA(Data!$A:$A)-1,0,-MIN(chtLen,COUNTA(Data!$A:$A)-1),1)

chtlen=Data!$C$3

chtperpass=OFFSET(chtCats,0,1)

Chart info:
Name=Data!$B$2

Values='Dynamic Graph Test.xls'!chtPerPass

Categories axis lable=='Dynamic Graph Test.xls'!chtCats

Thanks, any ideas would be greatly appreciated!

We store all of our data in a log, which I am considering the "second file". I would like a dynamic chart that displays values from the last 13 months of data from this log. I started a new file that will pull the monthly figures we need (example ='G:\QA\Micro Testing\[Micro Logs.xls]Listeria ''09'!$B$288) and enter them in the new "dynamic chart" file.

The main log ("second file") is formatted calculate values that we need as raw data is entered, so future months show a #DIV/0! error until values are entered. When this error is pulled into the new "dynamic chart", it counts it as a value and tries to add it to the graph.

I am trying to figure out how to set it up so that the only values graphed are ones that contain an actual date and number, not an error value. The information from my first post is from the new "dymanic chart".

Thanks!