If the issue appears to be related to RTC, then you can take AppScan out of the picture by connecting directly to the jts/admin page. Doing this will help validate whether or not RTC is configured correctly.
If the issue is reproducible by connecting directly to RTC, then the issue would lie in RTC and may not be related to AppScan.
If the issue is not reproducible, then the issue will most likely lie in AppScan.
Recommended data gathering and subsequent analysis steps
The majority of issues reported with this integration have historically been related to the LDAP configuration, thus the investigation will primarily focus in that area.
Collect the log and trace output detailed in the AppScan section of MustGather: Integration issues when using Rational Team Concert