ITS_ILLEGAL_FUNCTION_NAME SAP ABAP Runtime Error its illegal function name

ITS_ILLEGAL_FUNCTION_NAME is an ABAP runtime error which you may come across when using or developing within an SAP system. See below for the standard details explaining what it means and how you can avoid or fix this runtime error.

Short Dump Classification: A - ABAP Programming Error

You can view further information about a runtme error by using transaction code ST22 which will show you this and all runtime erros that have happen in your SAP system.

Also check out the Comments section below to view or add related contributions and example screen shots.

ITS_ILLEGAL_FUNCTION_NAME ABAP Runtime Error

If the error occurs in a non-modfied SAP template, you might be able to find a solution in the SAP Notes system.
If you have access to the SAP Notes system, check there first using the following keywords:
<runtime parameter> Template interpretation terminated, syntax error. Call transaction SE80 and correct the syntax error. In SE80, choose 'Internet Service' and navigate to the corresponding template. Take the service, theme and template name from the path of the template causing the error:
<runtime parameter>.
Remember to publish the corrected template on the 'INTERNAL' site in order to activate the change. Please see abap error for more details about the possible cause of this runtime error and how it could be avoided.

The specified function name is not allowed, or the function name is a reserved name.

HTMLB example, error ITS_ILLEGAL_FUNCTION_NAME
`function declare()` <- error, declare is reserved `end;`

`function my_declare()` <- Ok
`end;` Template <runtime parameter> contains syntax errors and therefore could not be compiled. Cause of error Invalid function name
The syntax error is in row <runtime parameter>, column <runtime parameter>
The HTMLB row with errors is:
<runtime parameter>