TruClient virtual users seem to lose connection after 7 iterations


We're experiencing issues where some virtual users suddenly appear to lose connectivity the TruClient replay engine.  The protocol is TruClient Firefox and the application uses AJAX. 


The behaviour seems to occur after exactly 7 iterations on most vusers. After that the scripts keep generating errors and we have to terminate the test manually. Unlike step-based errors where the snapshot shows the page where the error occurred, these snapshots show an error as possibly a LoadRunner / TruClient DLL.


Screenshot of the error snapshot:


I haven't been able to find any documentation on this error message or DLL.  Wondering whether this is the TruClient browser disconnecting or is it the script that is causing the issue.


Please advise, thanks