12.1 Migration problem - datebetween() function keeps throwing error

Question

Hello!  We just got done migrating our 11.5 code over to 12.1 and experienced this issue after running the application.
Apparently, in the BLS transaction (mainly in the "Conditional Action Block"), we have a datebetween function to determine which path the program should execute.  This worked fine in 11.5 but it keeps throwing this error
Unable to execute datebetween function, some internal exception occured. [null]
I even cleared the original datebetween function, copied and pasted the function straight from the SAP Help Documentation and I still get the same error.  It worked fine in 11.5
Any help would be greatly appreciated.
Thank you!

Answer 1

I actually figured out what the problem was:
if you use the datebetween() function with any invalid datetimes (such as "TimeUnavailable", "---" etc), it will throw this error.  Unlike 11.5, the paths and the datatypes (I realized from this) are extremely sensitive. 
Also, (just to add), when inserting values into an XML container, make sure the source document is <DocName>.Output.  Apparantly, 11.5 was allowing the source document to be similar to that of a repeater (<DocName>.Output{/Rowsets/Rowset/Row}).  This too will throw another exemption error.
Thank you guys for your help!