Append structure does not exist-cannot be deleted

Dear SAP Experts,

I have a structure /1CADMC/100000000053785LFA1 which was created by one of a program but was inactive. I tried to activate it but with errors.

The activation error logs:

Field XXX in table /1CADMC/100000000053785LFA1 is specified twice. Please check

Within this structure /1CADMC/100000000053785LFA1, i have found two APPEND STRUCTURES which caused the duplicate fields.

Unfortunately, I tried to delete one of the APPEND STRUCTURES, the system prompted that this structure does not exist (SE11).

I tried to experiment creating this append structure in SE11, the system prompted that this structure name already exist..

It seems like there is some kind of cache which need to be clear from the system.

Kindly help to advise how should I proceed to delete this append structure or activate the main structure.

Thank you!

Best Regards,

Bee Huang